System Administration Guide

For Red Hat Enterprise Linux 4

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Abstract

The System Administrator's Guide documents relevant information regarding the deployment, configuration and administration of Red Hat Enterprise Linux 4. It is oriented towards system administrators with a basic understanding of the system.

Introduction

Welcome to the System Administrators Guide.

The System Administrators Guide contains information on how to customize your Red Hat Enterprise Linux system to fit your needs. If you are looking for a step-by-step, task-oriented guide for configuring and customizing your system, this is the manual for you. This manual discusses many intermediate topics such as the following:

Setting up a network interface card (NIC)

Performing a Kickstart installation

Configuring Samba shares

Managing your software with RPM

Determining information about your system

Upgrading your kernel

This manual is divided into the following main categories:

Installation-Related Reference

File Systems Reference

Package Management

Network Configuration

System Configuration

System Monitoring

This guide assumes you have a basic understanding of your Red Hat Enterprise Linux system. If you need help installing Red Hat Enterprise Linux, refer to the Installation Guide. For more general information about system administration, refer to the Introduction to System Administration. If you need more advanced documentation such as an overview of file systems, refer to the Reference Guide. If you need security information, refer to the Security Guide.

1. Changes To This Manual

This manual has been reorganized for clarity and updated for the latest features of Red Hat Enterprise Linux 4. Some of the changes include:

Updated Kernel Modules and Manually Updating the Kernel Chapters

The Kernel Modules and the Upgrading the Kernel Manually chapters include updated information in regards to the 2.6 kernel. Special thanks to Arjan van de Ven for his hard work in helping to complete this chapter.

An Updated Network File System (NFS) Chapter

The Network File System (NFS) chapter has been revised and reorganized to include NFSv4. Special thanks to Steve Dickson for his hard work in helping to complete this chapter.

An Updated OProfile Chapter

The OProfile chapter has been revised and reorganized to include updated information in regards to the 2.6 kernel. Special thanks to Will Cohen for his hard work in helping to complete this chapter.

An Updated X Window System Chapter

The X Window System chapter has been revised to include information on the X11R6.8 release developed by the X.Org team.

Before reading this guide, you should be familiar with the contents of the Installation Guide concerning installation issues, the Introduction to System Administration for basic administration concepts, the System Administrators Guide for general customization instructions, and the Security Guide for security related instructions. This guide contains information about topics for advanced users.

2. Document Conventions

This manual uses several conventions to highlight certain words and phrases and draw attention to specific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts set. The Liberation Fonts set is also used in HTML editions if the set is installed on your system. If not, alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later include the Liberation Fonts set by default.

2.1. Typographic Conventions

Four typographic conventions are used to call attention to specific words and phrases. These conventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlight keys and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your current working directory, enter the cat my_next_bestselling_novel command at the shell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a key, all presented in mono-spaced bold and all distinguishable thanks to context.

Key combinations can be distinguished from an individual key by the plus sign that connects each part of a key combination. For example:

Press Enter to execute the command.

Press Ctrl+Alt+F2 to switch to a virtual terminal.

The first example highlights a particular key to press. The second example highlights a key combination: a set of three keys pressed simultaneously.

If source code is discussed, class names, methods, functions, variable names and returned values mentioned within a paragraph will be presented as above, in mono-spaced bold. For example:

File-related classes include filesystem for file systems, file for files, and dir for directories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialog box text; labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:

Choose System → Preferences → Mouse from the main menu bar to launch Mouse Preferences. In the Buttons tab, select the Left-handed mouse check box and click Close to switch the primary mouse button from the left to the right (making the mouse suitable for use in the left hand).

To insert a special character into a gedit file, choose Applications → Accessories → Character Map from the main menu bar. Next, choose Search → Find… from the Character Map menu bar, type the name of the character in the Search field and click Next. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the Copy button. Now switch back to your document and choose Edit → Paste from the gedit menu bar.

The above text includes application names; system-wide menu names and items; application-specific menu names; and buttons and text found within a GUI interface, all presented in proportional bold and all distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable or variable text. Italics denotes text you do not input literally or displayed text that changes depending on circumstance. For example:

To connect to a remote machine using ssh, type ssh username@domain.name at a shell prompt. If the remote machine is example.com and your username on that machine is john, type ssh john@example.com.

The mount -o remount file-system command remounts the named file system. For example, to remount the /home file system, the command is mount -o remount /home.

To see the version of a currently installed package, use the rpm -q package command. It will return a result as follows: package-version-release.

Note the words in bold italics above — username, domain.name, file-system, package, version and release. Each word is a placeholder, either for text you enter when issuing a command or for text displayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new and important term. For example:

Publican is a DocBook publishing system.

2.2. Pull-quote Conventions

Terminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus:

2.3. Notes and Warnings

Finally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note should have no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply to the current session, or services that need restarting before an update will apply. Ignoring a box labeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

3. More to Come

The System Administrators Guide is part of Red Hat, Inc's growing commitment to provide useful and timely support to Red Hat Enterprise Linux users. As new tools and applications are released, this guide will be expanded to include them.

3.1. Send in Your Feedback

If you find an error in the System Administrators Guide, or if you have thought of a way to make this manual better, we would love to hear from you! Please submit a report in Bugzilla (http://bugzilla.redhat.com/bugzilla/) against the component rh-sag.

Be sure to mention the manual's identifier:

rh-sag

By mentioning this manual's identifier, we know exactly which version of the guide you have.

If you have a suggestion for improving the documentation, try to be as specific as possible when describing it. If you have found an error, please include the section number and some of the surrounding text so we can find it easily.

Part I. Installation-Related Information

The Installation Guide discusses the installation of Red Hat Enterprise Linux and some basic post-installation troubleshooting. However, advanced installation options are covered in this manual. This part provides instructions for kickstart (an automated installation technique) and all related tools. Use this part in conjunction with the Installation Guide to perform any of these advanced installation tasks.

1.1. What are Kickstart Installations?

Many system administrators would prefer to use an automated installation method to install Red Hat Enterprise Linux on their machines. To answer this need, Red Hat, Inc created the kickstart installation method. Using kickstart, a system administrator can create a single file containing the answers to all the questions that would normally be asked during a typical installation.

Kickstart files can be kept on a single server system and read by individual computers during the installation. This installation method can support the use of a single kickstart file to install Red Hat Enterprise Linux on multiple machines, making it ideal for network and system administrators.

Kickstart provides a way for users to automate a Red Hat Enterprise Linux installation.

1.2. How Do You Perform a Kickstart Installation?

Kickstart installations can be performed using a local CD-ROM, a local hard drive, or via NFS, FTP, or HTTP.

To use kickstart, you must:

Create a kickstart file.

Create a boot media with the kickstart file or make the kickstart file available on the network.

Make the installation tree available.

Start the kickstart installation.

This chapter explains these steps in detail.

1.3. Creating the Kickstart File

The kickstart file is a simple text file, containing a list of items, each identified by a keyword. You can create it by editing a copy of the sample.ks file found in the RH-DOCS directory of the Red Hat Enterprise Linux Documentation CD, using the Kickstart Configurator application, or writing it from scratch. The Red Hat Enterprise Linux installation program also creates a sample kickstart file based on the options that you selected during installation. It is written to the file /root/anaconda-ks.cfg. You should be able to edit it with any text editor or word processor that can save files as ASCII text.

First, be aware of the following issues when you are creating your kickstart file:

Sections must be specified in order. Items within the sections do not have to be in a specific order unless otherwise specified. The section order is:

Omitting any required item results in the installation program prompting the user for an answer to the related item, just as the user would be prompted during a typical installation. Once the answer is given, the installation continues unattended (unless it finds another missing item).

Lines starting with a pound (or hash) sign (#) are treated as comments and are ignored.

For kickstart upgrades, the following items are required:

Language

Language support

Installation method

Device specification (if device is needed to perform the installation)

Keyboard setup

The upgrade keyword

Boot loader configuration

If any other items are specified for an upgrade, those items are ignored (note that this includes package selection).

1.4. Kickstart Options

The following options can be placed in a kickstart file. If you prefer to use a graphical interface for creating your kickstart file, use the Kickstart Configurator application. Refer to Chapter 2, Kickstart Configurator for details.

Note

If the option is followed by an equals mark (=), a value must be specified after it. In the example commands, options in brackets ([]) are optional arguments for the command.

autopart (optional)

Automatically create partitions — 1 GB or more root (/) partition, a swap partition, and an appropriate boot partition for the architecture. One or more of the default partition sizes can be redefined with the part directive.

ignoredisk (optional)

Causes the installer to ignore the specified disks. This is useful if you use autopartition and want to be sure that some disks are ignored. For example, without ignoredisk, attempting to deploy on a SAN-cluster the kickstart would fail, as the installer detects passive paths to the SAN that return no partition table.

The ignoredisk option is also useful if you have multiple paths to your disks.

The syntax is:

ignoredisk --drives=drive1,drive2,...

where driveN is one of sda, sdb,..., hda,... etc.

autostep (optional)

Similar to interactive except it goes to the next screen for you. It is used mostly for debugging.

auth or authconfig (required)

Sets up the authentication options for the system. It is similar to the authconfig command, which can be run after the install. By default, passwords are normally encrypted and are not shadowed.

--enablemd5

Use md5 encryption for user passwords.

--enablenis

Turns on NIS support. By default, --enablenis uses whatever domain it finds on the network. A domain should almost always be set by hand with the --nisdomain= option.

--nisdomain=

NIS domain name to use for NIS services.

--nisserver=

Server to use for NIS services (broadcasts by default).

--useshadow or --enableshadow

Use shadow passwords.

--enableldap

Turns on LDAP support in /etc/nsswitch.conf, allowing your system to retrieve information about users (UIDs, home directories, shells, etc.) from an LDAP directory. To use this option, you must install the nss_ldap package. You must also specify a server and a base DN (distinguished name) with --ldapserver= and --ldapbasedn=.

--enableldapauth

Use LDAP as an authentication method. This enables the pam_ldap module for authentication and changing passwords, using an LDAP directory. To use this option, you must have the nss_ldap package installed. You must also specify a server and a base DN with --ldapserver= and --ldapbasedn=.

--ldapserver=

If you specified either --enableldap or --enableldapauth, use this option to specify the name of the LDAP server to use. This option is set in the /etc/ldap.conf file.

--ldapbasedn=

If you specified either --enableldap or --enableldapauth, use this option to specify the DN in your LDAP directory tree under which user information is stored. This option is set in the /etc/ldap.conf file.

--enableldaptls

Use TLS (Transport Layer Security) lookups. This option allows LDAP to send encrypted usernames and passwords to an LDAP server before authentication.

--enablekrb5

Use Kerberos 5 for authenticating users. Kerberos itself does not know about home directories, UIDs, or shells. If you enable Kerberos, you must make users' accounts known to this workstation by enabling LDAP, NIS, or Hesiod or by using the /usr/sbin/useradd command to make their accounts known to this workstation. If you use this option, you must have the pam_krb5 package installed.

--krb5realm=

The Kerberos 5 realm to which your workstation belongs.

--krb5kdc=

The KDC (or KDCs) that serve requests for the realm. If you have multiple KDCs in your realm, separate their names with commas (,).

--krb5adminserver=

The KDC in your realm that is also running kadmind. This server handles password changing and other administrative requests. This server must be run on the master KDC if you have more than one KDC.

--enablehesiod

Enable Hesiod support for looking up user home directories, UIDs, and shells. More information on setting up and using Hesiod on your network is in /usr/share/doc/glibc-2.x.x/README.hesiod, which is included in the glibc package. Hesiod is an extension of DNS that uses DNS records to store information about users, groups, and various other items.

--hesiodlhs

The Hesiod LHS ("left-hand side") option, set in /etc/hesiod.conf. This option is used by the Hesiod library to determine the name to search DNS for when looking up information, similar to LDAP's use of a base DN.

--hesiodrhs

The Hesiod RHS ("right-hand side") option, set in /etc/hesiod.conf. This option is used by the Hesiod library to determine the name to search DNS for when looking up information, similar to LDAP's use of a base DN.

Tip

To look up user information for "jim", the Hesiod library looks up jim.passwd<LHS><RHS>, which should resolve to a TXT record that looks like what his passwd entry would look like (jim:*:501:501:Jungle Jim:/home/jim:/bin/bash). For groups, the situation is identical, except jim.group<LHS><RHS> would be used.

Looking up users and groups by number is handled by making "501.uid" a CNAME for "jim.passwd", and "501.gid" a CNAME for "jim.group". Note that the LHS and RHS do not have periods . put in front of them when the library determines the name for which to search, so the LHS and RHS usually begin with periods.

--enablesmbauth

Enables authentication of users against an SMB server (typically a Samba or Windows server). SMB authentication support does not know about home directories, UIDs, or shells. If you enable SMB, you must make users' accounts known to the workstation by enabling LDAP, NIS, or Hesiod or by using the /usr/sbin/useradd command to make their accounts known to the workstation. To use this option, you must have the pam_smb package installed.

--smbservers=

The name of the server(s) to use for SMB authentication. To specify more than one server, separate the names with commas (,).

--smbworkgroup=

The name of the workgroup for the SMB servers.

--enablecache

Enables the nscd service. The nscd service caches information about users, groups, and various other types of information. Caching is especially helpful if you choose to distribute information about users and groups over your network using NIS, LDAP, or hesiod.

bootloader (required)

Specifies how the GRUB boot loader should be installed. This option is required for both installations and upgrades. For upgrades, if GRUB is not the current boot loader, the boot loader is changed to GRUB. To preserve other boot loaders, use bootloader --upgrade.

--append=

Specifies kernel parameters. To specify multiple parameters, separate them with spaces. For example:

bootloader --location=mbr --append="hdd=ide-scsi ide=nodma"

--driveorder

Specify which drive is first in the BIOS boot order. For example:

bootloader --driveorder=sda,hda

--location=

Specifies where the boot record is written. Valid values are the following: mbr (the default), partition (installs the boot loader on the first sector of the partition containing the kernel), or none (do not install the boot loader).

--password=

Sets the GRUB boot loader password to the one specified with this option. This should be used to restrict access to the GRUB shell, where arbitrary kernel options can be passed.

--md5pass=

Similar to --password= except the password should already be encrypted.

--upgrade

Upgrade the existing boot loader configuration, preserving the old entries. This option is only available for upgrades.

clearpart (optional)

Removes partitions from the system, prior to creation of new partitions. By default, no partitions are removed.

Note

If the clearpart command is used, then the --onpart command cannot be used on a logical partition.

--all

Erases all partitions from the system.

--drives=

Specifies which drives to clear partitions from. For example, the following clears all the partitions on the first two drives on the primary IDE controller:

clearpart --drives=hda,hdb --all

--initlabel

Initializes the disk label to the default for your architecture (for example msdos for x86 and gpt for Itanium). It is useful so that the installation program does not ask if it should initialize the disk label if installing to a brand new hard drive.

--linux

Erases all Linux partitions.

--none (default)

Do not remove any partitions.

cmdline (optional)

Perform the installation in a completely non-interactive command line mode. Any prompts for interaction halts the install. This mode is useful on S/390 systems with the x3270 console.

device (optional)

On most PCI systems, the installation program autoprobes for Ethernet and SCSI cards properly. On older systems and some PCI systems, however, kickstart needs a hint to find the proper devices. The device command, which tells the installation program to install extra modules, is in this format:

device <type><moduleName> --opts=<options>

<type>

Replace with either scsi or eth

<moduleName>

Replace with the name of the kernel module which should be installed.

--opts=

Mount options to use for mounting the NFS export. Any options that can be specified in /etc/fstab for an NFS mount are allowed. The options are listed in the nfs(5) man page. Multiple options are separated with a comma.

driverdisk (optional)

Driver diskettes can be used during kickstart installations. You must copy the driver diskettes's contents to the root directory of a partition on the system's hard drive. Then you must use the driverdisk command to tell the installation program where to look for the driver disk.

driverdisk <partition> [--type=<fstype>]

Alternatively, a network location can be specified for the driver diskette:

This option corresponds to the Firewall Configuration screen in the installation program:

firewall --enabled|--disabled [--trust=] <device> [--port=]

--enabled

Reject incoming connections that are not in response to outbound requests, such as DNS replies or DHCP requests. If access to services running on this machine is needed, you can choose to allow specific services through the firewall.

--disabled

Do not configure any iptables rules.

--trust=

Listing a device here, such as eth0, allows all traffic coming from that device to go through the firewall. To list more than one device, use --trust eth0 --trust eth1. Do NOT use a comma-separated format such as --trust eth0, eth1.

<incoming>

Replace with one or more of the following to allow the specified services through the firewall.

--ssh

--telnet

--smtp

--http

--ftp

--port=

You can specify that ports be allowed through the firewall using the port:protocol format. For example, to allow IMAP access through your firewall, specify imap:tcp. Numeric ports can also be specified explicitly; for example, to allow UDP packets on port 1234 through, specify 1234:udp. To specify multiple ports, separate them by commas.

firstboot (optional)

Determine whether the Setup Agent starts the first time the system is booted. If enabled, the firstboot package must be installed. If not specified, this option is disabled by default.

--enable

The Setup Agent is started the first time the system boots.

--disable

The Setup Agent is not started the first time the system boots.

--reconfig

Enable the Setup Agent to start at boot time in reconfiguration mode. This mode enables the language, mouse, keyboard, root password, security level, time zone, and networking configuration options in addition to the default ones.

halt (optional)

Halt the system after the installation has successfully completed. This is similar to a manual installation, where anaconda displays a message and waits for the user to press a key before rebooting. During a kickstart installation, if no completion method is specified, the reboot option is used as default.

The halt option is roughly equivalent to the shutdown -h command.

For other completion methods, refer to the poweroff, reboot, and shutdown kickstart options.

install (optional)

Tells the system to install a fresh system rather than upgrade an existing system. This is the default mode. For installation, you must specify the type of installation from cdrom, harddrive, nfs, or url (for FTP or HTTP installations). The install command and the installation method command must be on separate lines.

cdrom

Install from the first CD-ROM drive on the system.

harddrive

Install from a Red Hat installation tree on a local drive, which must be either vfat or ext2.

--partition=

Partition to install from (such as, sdb2).

--dir=

Directory containing the RedHat directory of the installation tree.

For example:

harddrive --partition=hdb2 --dir=/tmp/install-tree

nfs

Install from the NFS server specified.

--server=

Server from which to install (hostname or IP).

--dir=

Directory containing the RedHat directory of the installation tree.

For example:

nfs --server=nfsserver.example.com --dir=/tmp/install-tree

url

Install from an installation tree on a remote server via FTP or HTTP.

For example:

url --url http://<server>/<dir>

or:

url --url ftp://<username>:<password>@<server>/<dir>

interactive (optional)

Uses the information provided in the kickstart file during the installation, but allow for inspection and modification of the values given. You are presented with each screen of the installation program with the values from the kickstart file. Either accept the values by clicking Next or change the values and click Next to continue. Refer to the autostep command.

keyboard (required)

Sets system keyboard type. Here is the list of available keyboards on i386, Itanium, and Alpha machines:

This list can also be found in the /usr/lib/python2.2/site-packages/rhpl/mouse.py file, which is part of the rhpl package.

If the mouse command is given without any arguments, or it is omitted, the installation program attempts to automatically detect the mouse. This procedure works for most modern mice.

network (optional)

Configures network information for the system. If the kickstart installation does not require networking (in other words, it is not installed over NFS, HTTP, or FTP), networking is not configured for the system. If the installation does require networking and network information is not provided in the kickstart file, the installation program assumes that the installation should be done over eth0 via a dynamic IP address (BOOTP/DHCP), and configures the final, installed system to determine its IP address dynamically. The network option configures networking information for kickstart installations via a network as well as for the installed system.

--bootproto=

One of dhcp, bootp, or static.

It defaults to dhcp. bootp and dhcp are treated the same.

The DHCP method uses a DHCP server system to obtain its networking configuration. As you might guess, the BOOTP method is similar, requiring a BOOTP server to supply the networking configuration. To direct a system to use DHCP:

network --bootproto=dhcp

To direct a machine to use BOOTP to obtain its networking configuration, use the following line in the kickstart file:

network --bootproto=bootp

The static method requires that you enter all the required networking information in the kickstart file. As the name implies, this information is static and are used during and after the installation. The line for static networking is more complex, as you must include all network configuration information on one line. You must specify the IP address, netmask, gateway, and nameserver. For example: (the "\" indicates that this should be read as one continuous line):

Used to select a specific Ethernet device for installation. Note that using --device= is not effective unless the kickstart file is a local file (such as ks=floppy), since the installation program configures the network to find the kickstart file. For example:

network --bootproto=dhcp --device=eth0

--ip=

IP address for the machine to be installed.

--gateway=

Default gateway as an IP address.

--nameserver=

Primary nameserver, as an IP address.

--nodns

Do not configure any DNS server.

--netmask=

Netmask for the installed system.

--hostname=

Hostname for the installed system.

--nostorage

Do not auto-probe storage devices such as ISCI, IDE or RAID.

part or partition (required for installs, ignored for upgrades)

Creates a partition on the system.

If more than one Red Hat Enterprise Linux installation exists on the system on different partitions, the installation program prompts the user and asks which installation to upgrade.

Warning

All partitions created are formatted as part of the installation process unless --noformat and --onpart are used.

The <mntpoint> is where the partition is mounted and must be of one of the following forms:

/<path>

For example, /, /usr, /home

swap

The partition is used as swap space.

To determine the size of the swap partition automatically, use the --recommended option:

swap --recommended

The minimum size of the automatically-generated swap partition is no smaller than the amount of RAM in the system and no larger than twice the amount of RAM in the system.

Using the recommended option yields a limitation of 8GB for the swap partition. If you want to create a larger swap partition, specify the correct size in the kickstart file or create the partitions manually.

raid.<id>

The partition is used for software RAID (refer to raid).

pv.<id>

The partition is used for LVM (refer to logvol).

--size=

The minimum partition size in megabytes. Specify an integer value here such as 500. Do not append the number with MB.

--grow

Tells the partition to grow to fill available space (if any), or up to the maximum size setting.

--maxsize=

The maximum partition size in megabytes when the partition is set to grow. Specify an integer value here, and do not append the number with MB.

--noformat

Tells the installation program not to format the partition, for use with the --onpart command.

--onpart= or --usepart=

Put the partition on the already existing device. For example:

partition /home --onpart=hda1

puts /home on /dev/hda1, which must already exist.

--ondisk= or --ondrive=

Forces the partition to be created on a particular disk. For example, --ondisk=sdb puts the partition on the second SCSI disk on the system.

--asprimary

Forces automatic allocation of the partition as a primary partition, or the partitioning fails.

--type= (replaced by fstype)

This option is no longer available. Use fstype.

--fstype=

Sets the file system type for the partition. Valid values are ext2, ext3, swap, and vfat.

--start=

Specifies the starting cylinder for the partition. It requires that a drive be specified with --ondisk= or ondrive=. It also requires that the ending cylinder be specified with --end= or the partition size be specified with --size=.

--end=

Specifies the ending cylinder for the partition. It requires that the starting cylinder be specified with --start=.

Note

If partitioning fails for any reason, diagnostic messages appear on virtual console 3.

poweroff (optional)

Shut down and power off the system after the installation has successfully completed. Normally during a manual installation, anaconda displays a message and waits for the user to press a key before rebooting. During a kickstart installation, if no completion method is specified, the reboot option is used as default.

The poweroff option is roughly equivalent to the shutdown -p command.

Note

The poweroff option is highly dependent on the system hardware in use. Specifically, certain hardware components such as the BIOS, APM (advanced power management), and ACPI (advanced configuration and power interface) must be able to interact with the system kernel. Contact your manufacturer for more information on you system's APM/ACPI abilities.

For other completion methods, refer to the halt, reboot, and shutdown kickstart options.

raid (optional)

Assembles a software RAID device. This command is of the form:

raid <mntpoint> --level=<level> --device=<mddevice><partitions*>

<mntpoint>

Location where the RAID file system is mounted. If it is /, the RAID level must be 1 unless a boot partition (/boot) is present. If a boot partition is present, the /boot partition must be level 1 and the root (/) partition can be any of the available types. The <partitions*> (which denotes that multiple partitions can be listed) lists the RAID identifiers to add to the RAID array.

--level=

RAID level to use (0, 1, or 5).

--device=

Name of the RAID device to use (such as md0 or md1). RAID devices range from md0 to md7, and each may only be used once.

--spares=

Specifies the number of spare drives allocated for the RAID array. Spare drives are used to rebuild the array in case of drive failure.

--fstype=

Sets the file system type for the RAID array. Valid values are ext2, ext3, swap, and vfat.

--noformat

Use an existing RAID device and do not format the RAID array.

--useexisting

Use an existing RAID device and reformat it.

The following example shows how to create a RAID level 1 partition for /, and a RAID level 5 for /usr, assuming there are three SCSI disks on the system. It also creates three swap partitions, one on each drive.

Shut down the system after the installation has successfully completed. During a kickstart installation, if no completion method is specified, the reboot option is used as default.

The shutdown option is roughly equivalent to the shutdown command.

For other completion methods, refer to the halt, poweroff, and reboot kickstart options.

skipx (optional)

If present, X is not configured on the installed system.

text (optional)

Perform the kickstart installation in text mode. Kickstart installations are performed in graphical mode by default.

timezone (required)

Sets the system time zone to <timezone> which may be any of the time zones listed by timeconfig.

timezone [--utc] <timezone>

--utc

If present, the system assumes the hardware clock is set to UTC (Greenwich Mean) time.

upgrade (optional)

Tells the system to upgrade an existing system rather than install a fresh system. You must specify one of cdrom, harddrive, nfs, or url (for FTP and HTTP) as the location of the installation tree. Refer to install for details.

xconfig (optional)

Configures the X Window System. If this option is not given, the user must configure X manually during the installation, if X was installed; this option should not be used if X is not installed on the final system.

--noprobe

Do not probe the monitor.

--card=

Use specified card; this card name should be from the list of cards in /usr/share/hwdata/Cards from the hwdata package. The list of cards can also be found on the X Configuration screen of the Kickstart Configurator. If this argument is not provided, the installation program probes the PCI bus for the card. Since AGP is part of the PCI bus, AGP cards are detected if supported. The probe order is determined by the PCI scan order of the motherboard.

--videoram=

Specifies the amount of video RAM the video card has.

--monitor=

Use specified monitor; monitor name should be from the list of monitors in /usr/share/hwdata/MonitorsDB from the hwdata package. The list of monitors can also be found on the X Configuration screen of the Kickstart Configurator. This is ignored if --hsync or --vsync is provided. If no monitor information is provided, the installation program tries to probe for it automatically.

--hsync=

Specifies the horizontal sync frequency of the monitor.

--vsync=

Specifies the vertical sync frequency of the monitor.

--defaultdesktop=

Specify either GNOME or KDE to set the default desktop (assumes that GNOME Desktop Environment and/or KDE Desktop Environment has been installed through %packages).

--startxonboot

Use a graphical login on the installed system.

--resolution=

Specify the default resolution for the X Window System on the installed system. Valid values are 640x480, 800x600, 1024x768, 1152x864, 1280x1024, 1400x1050, 1600x1200. Be sure to specify a resolution that is compatible with the video card and monitor.

--depth=

Specify the default color depth for the X Window System on the installed system. Valid values are 8, 16, 24, and 32. Be sure to specify a color depth that is compatible with the video card and monitor.

volgroup (optional)

Use to create a Logical Volume Management (LVM) group with the syntax:

volgroup <name><partition><options>

The options are as follows:

--noformat

Use an existing volume group and do not format it.

--useexisting

Use an existing volume group and reformat it.

Create the partition first, create the logical volume group, and then create the logical volume. For example:

If zerombr is specified, and yes is its sole argument, any invalid partition tables found on disks are initialized. This destroys all of the contents of disks with invalid partition tables. This command should be in the following format:

zerombr yes

No other format is effective.

%include

Use the %include /path/to/file command to include the contents of another file in the kickstart file as though the contents were at the location of the %include command in the kickstart file.

1.4.1. Advanced Partitioning Example

The following is a single, integrated example showing the clearpart, raid, part, volgroup, and logvol kickstart options in action:

This advanced example implements LVM over RAID, as well as the ability to resize various directories for future growth.

1.5. Package Selection

Use the %packages command to begin a kickstart file section that lists the packages you would like to install (this is for installations only, as package selection during upgrades is not supported).

Packages can be specified by group or by individual package name. The installation program defines several groups that contain related packages. Refer to the RedHat/base/comps.xml file on the first Red Hat Enterprise Linux CD-ROM for a list of groups. Each group has an id, user visibility value, name, description, and package list. In the package list, the packages marked as mandatory are always installed if the group is selected, the packages marked default are selected by default if the group is selected, and the packages marked optional must be specifically selected even if the group is selected to be installed.

In most cases, it is only necessary to list the desired groups and not individual packages. Note that the Core and Base groups are always selected by default, so it is not necessary to specify them in the %packages section.

As you can see, groups are specified, one to a line, starting with an @ symbol, a space, and then the full group name as given in the comps.xml file. Groups can also be specified using the id for the group, such as gnome-desktop. Specify individual packages with no additional characters (the dhcp line in the example above is an individual package).

You can also specify which packages not to install from the default package list:

-autofs

The following options are available for the %packages option:

--resolvedeps

Install the listed packages and automatically resolve package dependencies. If this option is not specified and there are package dependencies, the automated installation pauses and prompts the user. For example:

%packages --resolvedeps

--ignoredeps

Ignore the unresolved dependencies and install the listed packages without the dependencies. For example:

%packages --ignoredeps

--ignoremissing

Ignore the missing packages and groups instead of halting the installation to ask if the installation should be aborted or continued. For example:

%packages --ignoremissing

1.6. Pre-installation Script

You can add commands to run on the system immediately after the ks.cfg has been parsed. This section must be at the end of the kickstart file (after the commands) and must start with the %pre command. You can access the network in the %pre section; however, name service has not been configured at this point, so only IP addresses work.

Note

Note that the pre-install script is not run in the change root environment.

--interpreter /usr/bin/python

Allows you to specify a different scripting language, such as Python. Replace /usr/bin/python with the scripting language of your choice.

This script determines the number of hard drives in the system and writes a text file with a different partitioning scheme depending on whether it has one or two drives. Instead of having a set of partitioning commands in the kickstart file, include the line:

%include /tmp/part-include

The partitioning commands selected in the script are used.

Note

The pre-installation script section of kickstart cannot manage multiple install trees or source media. This information must be included for each created ks.cfg file, as the pre-installation script occurs during the second stage of the installation process.

1.7. Post-installation Script

You have the option of adding commands to run on the system once the installation is complete. This section must be at the end of the kickstart file and must start with the %post command. This section is useful for functions such as installing additional software and configuring an additional nameserver.

Note

If you configured the network with static IP information, including a nameserver, you can access the network and resolve IP addresses in the %post section. If you configured the network for DHCP, the /etc/resolv.conf file has not been completed when the installation executes the %post section. You can access the network, but you can not resolve IP addresses. Thus, if you are using DHCP, you must specify IP addresses in the %post section.

Note

The post-install script is run in a chroot environment; therefore, performing tasks such as copying scripts or RPMs from the installation media do not work.

--nochroot

Allows you to specify commands that you would like to run outside of the chroot environment.

The following example copies the file /etc/resolv.conf to the file system that was just installed.

%post --nochroot
cp /etc/resolv.conf /mnt/sysimage/etc/resolv.conf

--interpreter /usr/bin/python

Allows you to specify a different scripting language, such as Python. Replace /usr/bin/python with the scripting language of your choice.

1.8. Making the Kickstart File Available

A kickstart file must be placed in one of the following locations:

On a boot diskette

On a boot CD-ROM

On a network

Normally a kickstart file is copied to the boot diskette, or made available on the network. The network-based approach is most commonly used, as most kickstart installations tend to be performed on networked computers.

Let us take a more in-depth look at where the kickstart file may be placed.

1.8.1. Creating Kickstart Boot Media

Diskette-based booting is no longer supported in Red Hat Enterprise Linux. Installations must use CD-ROM or flash memory products for booting. However, the kickstart file may still reside on a diskette's top-level directory, and must be named ks.cfg.

To perform a CD-ROM-based kickstart installation, the kickstart file must be named ks.cfg and must be located in the boot CD-ROM's top-level directory. Since a CD-ROM is read-only, the file must be added to the directory used to create the image that is written to the CD-ROM. Refer to the Installation Guide for instructions on creating boot media; however, before making the file.iso image file, copy the ks.cfg kickstart file to the isolinux/ directory.

To perform a pen-based flash memory kickstart installation, the kickstart file must be named ks.cfg and must be located in the flash memory's top-level directory. Create the boot image first, and then copy the ks.cfg file.

For example, the following transfers a boot image to the pen drive (/dev/sda) using the dd command:

dd if=diskboot.img of=/dev/sda bs=1M

Note

Creation of USB flash memory pen drives for booting is possible, but is heavily dependent on system hardware BIOS settings. Refer to your hardware manufacturer to see if your system supports booting to alternate devices.

1.8.2. Making the Kickstart File Available on the Network

Network installations using kickstart are quite common, because system administrators can easily automate the installation on many networked computers quickly and painlessly. In general, the approach most commonly used is for the administrator to have both a BOOTP/DHCP server and an NFS server on the local network. The BOOTP/DHCP server is used to give the client system its networking information, while the actual files used during the installation are served by the NFS server. Often, these two servers run on the same physical machine, but they are not required to.

To perform a network-based kickstart installation, you must have a BOOTP/DHCP server on your network, and it must include configuration information for the machine on which you are attempting to install Red Hat Enterprise Linux. The BOOTP/DHCP server provides the client with its networking information as well as the location of the kickstart file.

If a kickstart file is specified by the BOOTP/DHCP server, the client system attempts an NFS mount of the file's path, and copies the specified file to the client, using it as the kickstart file. The exact settings required vary depending on the BOOTP/DHCP server you use.

Here is an example of a line from the dhcpd.conf file for the DHCP server:

filename"/usr/new-machine/kickstart/";
next-server blarg.redhat.com;

Note that you should replace the value after filename with the name of the kickstart file (or the directory in which the kickstart file resides) and the value after next-server with the NFS server name.

If the file name returned by the BOOTP/DHCP server ends with a slash ("/"), then it is interpreted as a path only. In this case, the client system mounts that path using NFS, and searches for a particular file. The file name the client searches for is:

<ip-addr>-kickstart

The <ip-addr> section of the file name should be replaced with the client's IP address in dotted decimal notation. For example, the file name for a computer with an IP address of 10.10.0.1 would be 10.10.0.1-kickstart.

Note that if you do not specify a server name, then the client system attempts to use the server that answered the BOOTP/DHCP request as its NFS server. If you do not specify a path or file name, the client system tries to mount /kickstart from the BOOTP/DHCP server and tries to find the kickstart file using the same <ip-addr>-kickstart file name as described above.

1.9. Making the Installation Tree Available

The kickstart installation must access an installation tree. An installation tree is a copy of the binary Red Hat Enterprise Linux CD-ROMs with the same directory structure.

If you are performing a CD-based installation, insert the Red Hat Enterprise Linux CD-ROM #1 into the computer before starting the kickstart installation.

If you are performing a hard drive installation, make sure the ISO images of the binary Red Hat Enterprise Linux CD-ROMs are on a hard drive in the computer.

If you are performing a network-based (NFS, FTP, or HTTP) installation, you must make the installation tree available over the network. Refer to the Preparing for a Network Installation section of the Installation Guide for details.

1.10. Starting a Kickstart Installation

To begin a kickstart installation, you must boot the system from boot media you have made or the Red Hat Enterprise Linux CD-ROM #1, and enter a special boot command at the boot prompt. The installation program looks for a kickstart file if the ks command line argument is passed to the kernel.

CD-ROM #1 and Diskette

The linux ks=floppy command also works if the ks.cfg file is located on a vfat or ext2 file system on a diskette and you boot from the Red Hat Enterprise Linux CD-ROM #1.

An alternate boot command is to boot off the Red Hat Enterprise Linux CD-ROM #1 and have the kickstart file on a vfat or ext2 file system on a diskette. To do so, enter the following command at the boot: prompt:

linux ks=hd:fd0:/ks.cfg

With Driver Disk

If you need to use a driver disk with kickstart, specify the dd option as well. For example, to boot off a boot diskette and use a driver disk, enter the following command at the boot: prompt:

linux ks=floppy dd

Boot CD-ROM

If the kickstart file is on a boot CD-ROM as described in Section 1.8.1, “Creating Kickstart Boot Media”, insert the CD-ROM into the system, boot the system, and enter the following command at the boot: prompt (where ks.cfg is the name of the kickstart file):

linux ks=cdrom:/ks.cfg

Other options to start a kickstart installation are as follows:

ks=nfs:<server>:/<path>

The installation program looks for the kickstart file on the NFS server <server>, as file <path>. The installation program uses DHCP to configure the Ethernet card. For example, if your NFS server is server.example.com and the kickstart file is in the NFS share /mydir/ks.cfg, the correct boot command would be ks=nfs:server.example.com:/mydir/ks.cfg.

ks=http://<server>/<path>

The installation program looks for the kickstart file on the HTTP server <server>, as file <path>. The installation program uses DHCP to configure the Ethernet card. For example, if your HTTP server is server.example.com and the kickstart file is in the HTTP directory /mydir/ks.cfg, the correct boot command would be ks=http://server.example.com/mydir/ks.cfg.

ks=floppy

The installation program looks for the file ks.cfg on a vfat or ext2 file system on the diskette in /dev/fd0.

ks=floppy:/<path>

The installation program looks for the kickstart file on the diskette in /dev/fd0, as file <path>.

ks=hd:<device>:/<file>

The installation program mounts the file system on <device> (which must be vfat or ext2), and look for the kickstart configuration file as <file> in that file system (for example, ks=hd:sda3:/mydir/ks.cfg).

ks=file:/<file>

The installation program tries to read the file <file> from the file system; no mounts are done. This is normally used if the kickstart file is already on the initrd image.

ks=cdrom:/<path>

The installation program looks for the kickstart file on CD-ROM, as file <path>.

ks

If ks is used alone, the installation program configures the Ethernet card to use DHCP. The kickstart file is read from the "bootServer" from the DHCP response as if it is an NFS server sharing the kickstart file. By default, the bootServer is the same as the DHCP server. The name of the kickstart file is one of the following:

If DHCP is specified and the boot file begins with a /, the boot file provided by DHCP is looked for on the NFS server.

If DHCP is specified and the boot file begins with something other then a /, the boot file provided by DHCP is looked for in the /kickstart directory on the NFS server.

If DHCP did not specify a boot file, then the installation program tries to read the file /kickstart/1.2.3.4-kickstart, where 1.2.3.4 is the numeric IP address of the machine being installed.

ksdevice=<device>

The installation program uses this network device to connect to the network. For example, to start a kickstart installation with the kickstart file on an NFS server that is connected to the system through the eth1 device, use the command ks=nfs:<server>:/<path> ksdevice=eth1 at the boot: prompt.

Kickstart Configurator allows you to create or modify a kickstart file using a graphical user interface, so that you do not have to remember the correct syntax of the file.

To use Kickstart Configurator, you must be running the X Window System. To start Kickstart Configurator, select Applications (the main menu on the
panel) => System Tools => Kickstart, or type the command /usr/sbin/system-config-kickstart.

As you are creating a kickstart file, you can select File => Preview at any time to review your current selections.

To start with an existing kickstart file, select File => Open and select the existing file.

2.1. Basic Configuration

Figure 2.1. Basic Configuration

Choose the language to use during the installation and as the default language to be used after installation from the Default Language menu.

Select the system keyboard type from the Keyboard menu.

Choose the mouse for the system from the Mouse menu. If No Mouse is selected, no mouse is configured. If Probe for Mouse is selected, the installation program tries to automatically detect the mouse. Probing works for most modern mice.

If the system has a two-button mouse, a three-button mouse can be emulated by selecting Emulate 3 Buttons. If this option is selected, simultaneously clicking the left and right mouse buttons are recognized as a middle mouse button click.

From the Time Zone menu, choose the time zone to use for the system. To configure the system to use UTC, select Use UTC clock.

Enter the desired root password for the system in the Root Password text entry box. Type the same password in the Confirm Password text box. The second field is to make sure you do not mistype the password and then realize you do not know what it is after you have completed the installation. To save the password as an encrypted password in the file, select Encrypt root password. If the encryption option is selected, when the file is saved, the plain text password that you typed are encrypted and written to the kickstart file. Do not type an already encrypted password and select to encrypt it. Because a kickstart file is a plain text file that can be easily read, it is recommended that an encrypted password be used.

To install languages in addition to the one selected from the Default Language pulldown menu. check them in the Language Support list. The language selected from the Default Language pulldown menu is used by default after installation; however, the default can be changed with the Language Configuration Tool (system-config-language) after installation.

Choosing Target Architecture specifies which specific hardware architecture distribution is used during installation.

Choosing Reboot system after installation reboots your system automatically after the installation is finished.

Kickstart installations are performed in graphical mode by default. To override this default and use text mode instead, select the Perform installation in text mode option.

You can perform a kickstart installation in interactive mode. This means that the installation program uses all the options pre-configured in the kickstart file, but it allows you to preview the options in each screen before continuing to the next screen. To continue to the next screen, click the Next button after you have approved the settings or change them before continuing the installation. To select this type of installation, select the Perform installation in interactive mode option.

2.2. Installation Method

Figure 2.2. Installation Method

The Installation Method screen allows you to choose whether to perform a new installation or an upgrade. If you choose upgrade, the Partition Information and Package Selection options are disabled. They are not supported for kickstart upgrades.

Choose the type of kickstart installation or upgrade screen from the following options:

CD-ROM — Choose this option to install or upgrade from the Red Hat Enterprise Linux CD-ROMs.

NFS — Choose this option to install or upgrade from an NFS shared directory. In the text field for the the NFS server, enter a fully-qualified domain name or IP address. For the NFS directory, enter the name of the NFS directory that contains the RedHat directory of the installation tree. For example, if the NFS server contains the directory /mirrors/redhat/i386/RedHat/, enter /mirrors/redhat/i386/ for the NFS directory.

FTP — Choose this option to install or upgrade from an FTP server. In the FTP server text field, enter a fully-qualified domain name or IP address. For the FTP directory, enter the name of the FTP directory that contains the RedHat directory. For example, if the FTP server contains the directory /mirrors/redhat/i386/RedHat/, enter /mirrors/redhat/i386/ for the FTP directory. If the FTP server requires a username and password, specify them as well.

HTTP — Choose this option to install or upgrade from an HTTP server. In the text field for the HTTP server, enter the fully-qualified domain name or IP address. For the HTTP directory, enter the name of the HTTP directory that contains the RedHat directory. For example, if the HTTP server contains the directory /mirrors/redhat/i386/RedHat/, enter /mirrors/redhat/i386/ for the HTTP directory.

Hard Drive — Choose this option to install or upgrade from a hard drive. Hard drive installations require the use of ISO (or CD-ROM) images. Be sure to verify that the ISO images are intact before you start the installation. To verify them, use an md5sum program as well as the linux mediacheck boot option as discussed in the Installation Guide. Enter the hard drive partition that contains the ISO images (for example, /dev/hda1) in the Hard Drive Partition text box. Enter the directory that contains the ISO images in the Hard Drive Directory text box.

2.3. Boot Loader Options

Figure 2.3. Boot Loader Options

GRUB is the default boot loader for Red Hat Enterprise Linux. If you do not want to install a boot loader, select Do not install a boot loader. If you choose not to install a boot loader, make sure you create a boot diskette or have another way to boot your system, such as a third-party boot loader.

You must choose where to install the boot loader (the Master Boot Record or the first sector of the /boot partition). Install the boot loader on the MBR if you plan to use it as your boot loader.

To pass any special parameters to the kernel to be used when the system boots, enter them in the Kernel parameters text field. For example, if you have an IDE CD-ROM Writer, you can tell the kernel to use the SCSI emulation driver that must be loaded before using cdrecord by configuring hdd=ide-scsi as a kernel parameter (where hdd is the CD-ROM device).

You can password protect the GRUB boot loader by configuring a GRUB password. Select Use GRUB password, and enter a password in the Password field. Type the same password in the Confirm Password text field. To save the password as an encrypted password in the file, select Encrypt GRUB password. If the encryption option is selected, when the file is saved, the plain text password that you typed are encrypted and written to the kickstart file. If type an already encrypted password, unselect to encrypt it.

If Upgrade an existing installation is selected on the Installation Method page, select Upgrade existing boot loader to upgrade the existing boot loader configuration, while preserving the old entries.

2.4. Partition Information

Figure 2.4. Partition Information

Select whether or not to clear the Master Boot Record (MBR). Choose to remove all existing partitions, remove all existing Linux partitions, or preserve existing partitions.

To initialize the disk label to the default for the architecture of the system (for example, msdos for x86 and gpt for Itanium), select Initialize the disk label if you are installing on a brand new hard drive.

2.4.1. Creating Partitions

To create a partition, click the Add button. The Partition Options window shown in Figure 2.5, “Creating Partitions” appears. Choose the mount point, file system type, and partition size for the new partition. Optionally, you can also choose from the following:

In the Additional Size Options section, choose to make the partition a fixed size, up to a chosen size, or fill the remaining space on the hard drive. If you selected swap as the file system type, you can select to have the installation program create the swap partition with the recommended size instead of specifying a size.

Force the partition to be created as a primary partition.

Create the partition on a specific hard drive. For example, to make the partition on the first IDE hard disk (/dev/hda), specify hda as the drive. Do not include /dev in the drive name.

Use an existing partition. For example, to make the partition on the first partition on the first IDE hard disk (/dev/hda1), specify hda1 as the partition. Do not include /dev in the partition name.

Format the partition as the chosen file system type.

Figure 2.5. Creating Partitions

To edit an existing partition, select the partition from the list and click the Edit button. The same Partition Options window appears as when you chose to add a partition as shown in Figure 2.5, “Creating Partitions”, except it reflects the values for the selected partition. Modify the partition options and click OK.

To delete an existing partition, select the partition from the list and click the Delete button.

2.4.1.1. Creating Software RAID Partitions

To create a software RAID partition, use the following steps:

Click the RAID button.

Select Create a software RAID partition.

Configure the partitions as previously described, except select Software RAID as the file system type. Also, you must specify a hard drive on which to make the partition or specify an existing partition to use.

Figure 2.6. Creating a Software RAID Partition

Repeat these steps to create as many partitions as needed for your RAID setup. All of your partitions do not have to be RAID partitions.

After creating all the partitions needed to form a RAID device, follow these steps:

Click the RAID button.

Select Create a RAID device.

Select a mount point, file system type, RAID device name, RAID level, RAID members, number of spares for the software RAID device, and whether to format the RAID device.

Figure 2.7. Creating a Software RAID Device

Click OK to add the device to the list.

2.5. Network Configuration

Figure 2.8. Network Configuration

If the system to be installed via kickstart does not have an Ethernet card, do not configure one on the Network Configuration page.

Networking is only required if you choose a networking-based installation method (NFS, FTP, or HTTP). Networking can always be configured after installation with the Network Administration Tool (system-config-network). Refer to Chapter 17, Network Configuration for details.

For each Ethernet card on the system, click Add Network Device and select the network device and network type for the device. Select eth0 to configure the first Ethernet card, eth1 for the second Ethernet card, and so on.

2.6. Authentication

Figure 2.9. Authentication

In the Authentication section, select whether to use shadow passwords and MD5 encryption for user passwords. These options are highly recommended and chosen by default.

The Authentication Configuration options allow you to configure the following methods of authentication:

NIS

LDAP

Kerberos 5

Hesiod

SMB

Name Switch Cache

These methods are not enabled by default. To enable one or more of these methods, click the appropriate tab, click the checkbox next to Enable, and enter the appropriate information for the authentication method. Refer to Chapter 26, Authentication Configuration for more information about the options.

2.7. Firewall Configuration

The Firewall Configuration window is similar to the screen in the installation program and the Security Level Configuration Tool.

Figure 2.10. Firewall Configuration

If Disable firewall is selected, the system allows complete access to any active services and ports. No connections to the system are refused or denied.

Selecting Enable firewall configures the system to reject incoming connections that are not in response to outbound requests, such as DNS replies or DHCP requests. If access to services running on this machine is required, you can choose to allow specific services through the firewall.

Only devices configured in the Network Configuration section are listed as available Trusted devices. Connections from any devices selected in the list are accepted by the system. For example, if eth1 only receives connections from internal system, you might want to allow connections from it.

If a service is selected in the Trusted services list, connections for the service are accepted and processed by the system.

In the Other ports text field, list any additional ports that should be opened for remote access. Use the following format: port:protocol. For example, to allow IMAP access through the firewall, specify imap:tcp. Specify numeric ports can also be specified; to allow UDP packets on port 1234 through the firewall, enter 1234:udp. To specify multiple ports, separate them with commas.

2.7.1. SELinux Configuration

Although configuration for SELinux is not specified in the Kickstart Configurator, kickstart enables SELinux in enforcing mode by default if the selinux parameter is omitted from the kickstart file.

2.8. Display Configuration

If you are installing the X Window System, you can configure it during the kickstart installation by checking the Configure the X Window System option on the Display Configuration window as shown in Figure 2.11, “X Configuration - General”. If this option is not chosen, the X configuration options are disabled and the skipx option is written to the kickstart file.

2.8.1. General

The first step in configuring X is to choose the default color depth and resolution. Select them from their respective pulldown menus. Be sure to specify a color depth and resolution that is compatible with the video card and monitor for the system.

Figure 2.11. X Configuration - General

If you are installing both the GNOME and KDE desktops, you must choose which desktop should be the default. If only one desktop is to be installed, be sure to choose it. Once the system is installed, users can choose which desktop they want to be their default.

Next, choose whether to start the X Window System when the system is booted. This option starts the system in runlevel 5 with the graphical login screen. After the system is installed, this can be changed by modifying the /etc/inittab configuration file.

Also select whether to start the Setup Agent the first time the system is rebooted. It is disabled by default, but the setting can be changed to enabled or enabled in reconfiguration mode. Reconfiguration mode enables the language, mouse, keyboard, root password, security level, time zone, and networking configuration options in addition to the default ones.

2.8.2. Video Card

Probe for video card is selected by default. Accept this default to have the installation program probe for the video card during installation. Probing works for most modern video cards. If this option is selected and the installation program cannot successfully probe the video card, the installation program stops at the video card configuration screen. To continue the installation process, select your video card from the list and click Next.

Alternatively, you can select the video card from the list on the Video Card tab as shown in Figure 2.12, “X Configuration - Video Card”. Specify the amount of video RAM the selected video card has from the Video Card RAM pulldown menu. These values are used by the installation program to configure the X Window System.

Figure 2.12. X Configuration - Video Card

2.8.3. Monitor

Probe for monitor is selected by default. Accept this default to have the installation program probe for the monitor during installation. Probing works for most modern monitors. If this option is selected and the installation program cannot successfully probe the monitor, the installation program stops at the monitor configuration screen. To continue the installation process, select your monitor from the list and click Next.

Alternatively, you can select your monitor from the list. You can also specify the horizontal and vertical sync rates instead of selecting a specific monitor by checking the Specify hysnc and vsync instead of monitor option. This option is useful if the monitor for the system is not listed. Notice that when this option is enabled, the monitor list is disabled.

2.9. Package Selection

Figure 2.14. Package Selection

The Package Selection window allows you to choose which package groups to install.

There are also options available to resolve and ignore package dependencies automatically.

Currently, Kickstart Configurator does not allow you to select individual packages. To install individual packages, modify the %packages section of the kickstart file after you save it. Refer to Section 1.5, “Package Selection” for details.

2.10. Pre-Installation Script

Figure 2.15. Pre-Installation Script

You can add commands to run on the system immediately after the kickstart file has been parsed and before the installation begins. If you have configured the network in the kickstart file, the network is enabled before this section is processed. To include a pre-installation script, type it in the text area.

To specify a scripting language to use to execute the script, select the Use an interpreter option and enter the interpreter in the text box beside it. For example, /usr/bin/python2.2 can be specified for a Python script. This option corresponds to using %pre --interpreter /usr/bin/python2.2 in your kickstart file.

Warning

Do not include the %pre command. It is added for you.

2.11. Post-Installation Script

Figure 2.16. Post-Installation Script

You can also add commands to execute on the system after the installation is completed. If the network is properly configured in the kickstart file, the network is enabled, and the script can include commands to access resources on the network. To include a post-installation script, type it in the text area.

Warning

Do not include the %post command. It is added for you.

For example, to change the message of the day for the newly installed system, add the following command to the %post section:

2.11.1. Chroot Environment

To run the post-installation script outside of the chroot environment, click the checkbox next to this option on the top of the Post-Installation window. This is equivalent to using the --nochroot option in the %post section.

To make changes to the newly installed file system, within the post-installation section, but outside of the chroot environment, you must prepend the directory name with /mnt/sysimage/.

For example, if you select Run outside of the chroot environment, the previous example must be changed to the following:

echo "Hackers will be punished!" > /mnt/sysimage/etc/motd

2.11.2. Use an Interpreter

To specify a scripting language to use to execute the script, select the Use an interpreter option and enter the interpreter in the text box beside it. For example, /usr/bin/python2.2 can be specified for a Python script. This option corresponds to using %post --interpreter /usr/bin/python2.2 in your kickstart file.

2.12. Saving the File

To review the contents of the kickstart file after you have finished choosing your kickstart options, select File => Preview from the pull-down menu.

Figure 2.17. Preview

To save the kickstart file, click the Save to File button in the preview window. To save the file without previewing it, select File => Save File or press Ctrl+S. A dialog box appears. Select where to save the file.

Red Hat Enterprise Linux allows for installation over a network using the NFS, FTP, or HTTP protocols. A network installation can be started from a boot CD-ROM, a bootable flash memory drive, or by using the askmethod boot option with the Red Hat Enterprise Linux CD #1. Alternatively, if the system to be installed contains a network interface card (NIC) with Pre-Execution Environment (PXE) support, it can be configured to boot from files on another networked system rather than local media such as a CD-ROM.

For a PXE network installation, the client's NIC with PXE support sends out a broadcast request for DHCP information. The DHCP server provides the client with an IP address, other network information such as name server, the IP address or hostname of the tftp server (which provides the files necessary to start the installation program), and the location of the files on the tftp server. This is possible because of PXELINUX, which is part of the syslinux package.

The following steps must be performed to prepare for a PXE installation:

3.1. Setting up the Network Server

First, configure an NFS, FTP, or HTTP server to export the entire installation tree for the version and variant of Red Hat Enterprise Linux to be installed. Refer to the section Preparing for a Network Installation in the Installation Guide for detailed instructions.

3.2. PXE Boot Configuration

The next step is to copy the files necessary to start the installation to the tftp server so they can be found when the client requests them. The tftp server is usually the same server as the network server exporting the installation tree.

To copy these files, run the Network Booting Tool on the NFS, FTP, or HTTP server. A separate PXE server is not necessary.

To use the graphical version of the Network Booting Tool, you must be running the X Window System, have root privileges, and have the system-config-netboot RPM package installed. To start the Network Booting Tool from the desktop, go to Applications (the main menu on the
panel) => System Settings => Server Settings => Network Booting Service. Or, type the command system-config-netboot at a shell prompt (for example, in an XTerm or a GNOME terminal).

If starting the Network Booting Tool for the first time, select Network Install from the First Time Druid. Otherwise, select Configure => Network Installation from the pulldown menu, and then click Add. The dialog in Figure 3.1, “Network Installation Setup” is displayed.

Figure 3.1. Network Installation Setup

Operating system identifier — Provide a unique name using one word to identify the Red Hat Enterprise Linux version and variant. It is used as the directory name in the /tftpboot/linux-install/ directory.

Description — Provide a brief description of the Red Hat Enterprise Linux version and variant.

Selects protocol for installation — Selects NFS, FTP, or HTTP as the network installation type depending on which one was configured previously. If FTP is selected and anonymous FTP is not being used, uncheck Anonymous FTP and provide a valid username and password combination.

Kickstart — Specify the location of the kickstart file. The file can be a URL or a file stored locally (diskette). The kickstart file can be created with the Kickstart Configurator. Refer to Chapter 2, Kickstart Configurator for details.

Server — Provide the IP address or domain name of the NFS, FTP, or HTTP server.

Location — Provide the directory shared by the network server. If FTP or HTTP was selected, the directory must be relative to the default directory for the FTP server or the document root for the HTTP server. For all network installations, the directory provided must contain the RedHat/ directory of the installation tree.

After clicking OK, the initrd.img and vmlinuz files necessary to boot the installation program are transfered from images/pxeboot/ in the provided installation tree to /tftpboot/linux-install/<os-identifier>/ on the tftp server (the one you are running the Network Booting Tool on).

3.2.1. Command Line Configuration

If the network server is not running X, the pxeos command line utility, which is part of the system-config-netboot package, can be used to configure the tftp server files :

-p <NFS|HTTP|FTP> — Specify which of the NFS, FTP, or HTTP protocols to use for installation. Only one may be specified. This corresponds to the Select protocol for installation menu in Figure 3.1, “Network Installation Setup”.

-D <0|1> — Specify "0" which indicates that it is not a diskless configuration since pxeos can be used to configure a diskless environment as well.

-k<kernel> — Provide the specific kernel version of the server installation tree for booting.

-K<kickstart> — Provide the location of the kickstart file, if available.

<os-identifer> — Specify the OS identifier, which is used as the directory name in the /tftpboot/linux-install/ directory. This corresponds to the Operating system identifier field in Figure 3.1, “Network Installation Setup”.

If FTP is selected as the installation protocol and anonymous login is not available, specify a username and password for login, with the following options before <os-identifer> in the previous command:

-A 0 -u <username> -p <password>

For more information on command line options available for the pxeos command, refer to the pxeos man page.

Hostname or IP Address/Subnet — The IP address, fully qualified hostname, or a subnet of systems that should be allowed to connect to the PXE server for installations.

Operating System — The operating system identifier to install on this client. The list is populated from the network install instances created from the Network Installation Dialog.

Serial Console — This option allows use of a serial console.

Kickstart File — The location of a kickstart file to use, such as http://server.example.com/kickstart/ks.cfg. This file can be created with the Kickstart Configurator. Refer to Chapter 2, Kickstart Configurator for details.

Ignore the Snapshot name and Ethernet options. They are only used for diskless environments. For more information on configuring a diskless environment, refer to Chapter 4, Diskless Environments for details.

3.3.1. Command Line Configuration

If the network server is not running X, the pxeboot utility, a part of the system-config-netboot package, can be used to add hosts which are allowed to connect to the PXE server:

Chapter 4. Diskless Environments

Some networks require multiple systems with the same configuration. They also require that these systems be easy to reboot, upgrade, and manage. One solution is to use a diskless environment in which most of the operating system, which can be read-only, is shared from a central server between the clients. The individual clients have their own directories on the central server for the rest of the operating system, which must be read/write. Each time the client boots, it mounts most of the OS from the NFS server as read-only and another directory as read-write. Each client has its own read-write directory so that one client can not affect the others.

The following steps are necessary to configure Red Hat Enterprise Linux to run on a diskless client:

Install Red Hat Enterprise Linux on a system so that the files can be copied to the NFS server. (Refer to the Installation Guide for details.) Any software to be used on the clients must be installed on this system and the busybox-anaconda package must be installed.

Create a directory on the NFS server to contain the diskless environment such as /diskless/i386/RHEL4-AS/. For example:

mkdir -p /diskless/i386/RHEL4-AS/

This directory is referred to as the diskless directory.

Create a subdirectory of this directory named root/:

mkdir -p /diskless/i386/RHEL4-AS/root/

Copy Red Hat Enterprise Linux from the client system to the server using rsync. For example:

Replace * with one of the hostname formats discussed in Section 21.3.2, “Hostname Formats”. Make the hostname declaration as specific as possible, so unwanted systems can not access the NFS mount.

If the NFS service is not running, start it:

service nfs start

If the NFS service is already running, reload the configuration file:

service nfs reload

4.2. Finish Configuring the Diskless Environment

To use the graphical version of the Network Booting Tool, you must be running the X Window System, have root privileges, and have the system-config-netboot RPM package installed. To start the Network Booting Tool from the desktop, go to Applications (the main menu on the
panel) => System Settings => Server Settings => Network Booting Service. Or, type the command system-config-netboot at a shell prompt (for example, in an XTerm or a GNOME terminal).

If starting the Network Booting Tool for the first time, select Diskless from the First Time Druid. Otherwise, select Configure => Diskless from the pull-down menu, and then click Add.

A wizard appears to step you through the process:

Click Forward on the first page.

On the Diskless Identifier page, enter a Name and Description for the diskless environment. Click Forward.

The kernel versions installed in the diskless environment are listed. Select the kernel version to boot on the diskless system.

Click Apply to finish the configuration.

After clicking Apply, the diskless kernel and image file are created based on the kernel selected. They are copied to the PXE boot directory /tftpboot/linux-install/<os-identifier>/. The directory snapshot/ is created in the same directory as the root/ directory (for example, /diskless/i386/RHEL4-AS/snapshot/) with a file called files in it. This file contains a list of files and directories that must be read/write for each diskless system. Do not modify this file. If additional entries must be added to the list, create a files.custom file in the same directory as the files file, and add each additional file or directory on a separate line.

4.3. Adding Hosts

Each diskless client must have its own snapshot directory on the NFS server that is used as its read/write file system. The Network Booting Tool can be used to create these snapshot directories.

Snapshot name — Provide a subdirectory name to be used to store all of the read/write content for the host.

Ethernet — Select the Ethernet device on the host to use to mount the diskless environment. If the host only has one Ethernet card, select eth0.

Ignore the Kickstart File option. It is only used for PXE installations.

Figure 4.1. Add Diskless Host

In the existing snapshot/ directory in the diskless directory, a subdirectory is created with the Snapshot name specified as the file name. Then, all of the files listed in snapshot/files and snapshot/files.custom are copied copy from the root/ directory to this new directory.

4.4. Booting the Hosts

Consult the documentation for your PXE card to configure the host to boot via PXE.

When the diskless client boots, it mounts the remote root/ directory in the diskless directory as read-only. It also mounts its individual snapshot directory as read/write. Then it mounts all the files and directories in the files and files.custom files using the mount -o bind over the read-only diskless directory to allow applications to write to the root directory of the diskless environment if they need to.

When things go wrong, there are ways to fix problems. However, these methods require that you understand the system well. This chapter describes how to boot into rescue mode, single-user mode, and emergency mode, where you can use your own knowledge to repair the system.

5.1. Common Problems

You might need to boot into one of these recovery modes for any of the following reasons:

You are unable to boot normally into Red Hat Enterprise Linux (runlevel 3 or 5).

You are having hardware or software problems, and you want to get a few important files off of your system's hard drive.

You forgot the root password.

5.1.1. Unable to Boot into Red Hat Enterprise Linux

This problem is often caused by the installation of another operating system after you have installed Red Hat Enterprise Linux. Some other operating systems assume that you have no other operating system(s) on your computer. They overwrite the Master Boot Record (MBR) that originally contained the GRUB boot loader. If the boot loader is overwritten in this manner, you cannot boot Red Hat Enterprise Linux unless you can get into rescue mode and reconfigure the boot loader.

Another common problem occurs when using a partitioning tool to resize a partition or create a new partition from free space after installation, and it changes the order of your partitions. If the partition number of your / partition changes, the boot loader might not be able to find it to mount the partition. To fix this problem, boot in rescue mode and modify the /boot/grub/grub.conf file.

5.1.2. Hardware/Software Problems

This category includes a wide variety of different situations. Two examples include failing hard drives and specifying an invalid root device or kernel in the boot loader configuration file. If either of these occur, you might not be able to reboot into Red Hat Enterprise Linux. However, if you boot into one of the system recovery modes, you might be able to resolve the problem or at least get copies of your most important files.

5.1.3. Root Password

What can you do if you forget your root password? To reset it to a different password, boot into rescue mode or single-user mode, and use the passwd command to reset the root password.

5.2. Booting into Rescue Mode

Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment entirely from CD-ROM, or some other boot method, instead of the system's hard drive.

As the name implies, rescue mode is provided to rescue you from something. During normal operation, your Red Hat Enterprise Linux system uses files located on your system's hard drive to do everything — run programs, store your files, and more.

However, there may be times when you are unable to get Red Hat Enterprise Linux running completely enough to access files on your system's hard drive. Using rescue mode, you can access the files stored on your system's hard drive, even if you cannot actually run Red Hat Enterprise Linux from that hard drive.

To boot into rescue mode, you must be able to boot the system using one of the following methods[1]:

By booting the system from an installation boot CD-ROM.

By booting the system from other installation boot media, such as USB flash devices.

By booting the system from the Red Hat Enterprise Linux CD-ROM #1.

Once you have booted using one of the described methods, add the keyword rescue as a kernel parameter. For example, for an x86 system, type the following command at the installation boot prompt:

linux rescue

You are prompted to answer a few basic questions, including which language to use. It also prompts you to select where a valid rescue image is located. Select from Local CD-ROM, Hard Drive, NFS image, FTP, or HTTP. The location selected must contain a valid installation tree, and the installation tree must be for the same version of Red Hat Enterprise Linux as the Red Hat Enterprise Linux disk from which you booted. If you used a boot CD-ROM or other media to start rescue mode, the installation tree must be from the same tree from which the media was created. For more information about how to setup an installation tree on a hard drive, NFS server, FTP server, or HTTP server, refer to the earlier section of this guide.

If you select a rescue image that does not require a network connection, you are asked whether or not you want to establish a network connection. A network connection is useful if you need to backup files to a different computer or install some RPM packages from a shared network location, for example.

The following message is displayed:

The rescue environment will now attempt to find your Linux installation and mount it under the directory /mnt/sysimage. You can then make any changes required to your system. If you want to proceed with this step choose 'Continue'. You can also choose to mount your file systems read-only instead of read-write by choosing 'Read-only'. If for some reason this process fails you can choose 'Skip' and this step will be skipped and you will go directly to a command shell.

If you select Continue, it attempts to mount your file system under the directory /mnt/sysimage/. If it fails to mount a partition, it notifies you. If you select Read-Only, it attempts to mount your file system under the directory /mnt/sysimage/, but in read-only mode. If you select Skip, your file system is not mounted. Choose Skip if you think your file system is corrupted.

Once you have your system in rescue mode, a prompt appears on VC (virtual console) 1 and VC 2 (use the Ctrl-Alt-F1 key combination to access VC 1 and Ctrl-Alt-F2 to access VC 2):

sh-3.00b#

If you selected Continue to mount your partitions automatically and they were mounted successfully, you are in single-user mode.

Even if your file system is mounted, the default root partition while in rescue mode is a temporary root partition, not the root partition of the file system used during normal user mode (runlevel 3 or 5). If you selected to mount your file system and it mounted successfully, you can change the root partition of the rescue mode environment to the root partition of your file system by executing the following command:

chroot /mnt/sysimage

This is useful if you need to run commands such as rpm that require your root partition to be mounted as /. To exit the chroot environment, type exit to return to the prompt.

If you selected Skip, you can still try to mount a partition or LVM2 logical volume manually inside rescue mode by creating a directory such as /foo, and typing the following command:

mount -t ext3 /dev/mapper/VolGroup00-LogVol02/foo

In the above command, /foo is a directory that you have created and /dev/mapper/VolGroup00-LogVol02 is the LVM2 logical volume you want to mount. If the partition is of type ext2, replace ext3 with ext2.

If you do not know the names of all physical partitions, use the following command to list them:

fdisk -l

If you do not know the names of all LVM2 physical volumes, volume groups, or logical volumes, use the following commands to list them:

pvdisplay

vgdisplay

lvdisplay

From the prompt, you can run many useful commands, such as:

ssh, scp, and ping if the network is started

dump and restore for users with tape drives

parted and fdisk for managing partitions

rpm for installing or upgrading software

joe for editing configuration files

Note

If you try to start other popular editors such as emacs, pico, or vi, the joe editor is started.

5.2.1. Reinstalling the Boot Loader

In many cases, the GRUB boot loader can mistakenly be deleted, corrupted, or replaced by other operating systems.

The following steps detail the process on how GRUB is reinstalled on the master boot record:

Boot the system from an installation boot medium.

Type linux rescue at the installation boot prompt to enter the rescue environment.

Type chroot /mnt/sysimage to mount the root partition.

Type /sbin/grub-install /dev/hda to reinstall the GRUB boot loader, where /dev/hda is the boot partition.

Review the /boot/grub/grub.conf file, as additional entries may be needed for GRUB to control additional operating systems.

Reboot the system.

5.3. Booting into Single-User Mode

One of the advantages of single-user mode is that you do not need a boot CD-ROM; however, it does not give you the option to mount the file systems as read-only or not mount them at all.

If your system boots, but does not allow you to log in when it has completed booting, try single-user mode.

In single-user mode, your computer boots to runlevel 1. Your local file systems are mounted, but your network is not activated. You have a usable system maintenance shell. Unlike rescue mode, single-user mode automatically tries to mount your file system. Do not use single-user mode if your file system cannot be mounted successfully. You cannot use single-user mode if the runlevel 1 configuration on your system is corrupted.

On an x86 system using GRUB, use the following steps to boot into single-user mode:

At the GRUB splash screen at boot time, press any key to enter the GRUB interactive menu.

Select Red Hat Enterprise Linux with the version of the kernel that you wish to boot and type a to append the line.

Go to the end of the line and type single as a separate word (press the Spacebar and then type single). Press Enter to exit edit mode.

5.4. Booting into Emergency Mode

In emergency mode, you are booted into the most minimal environment possible. The root file system is mounted read-only and almost nothing is set up. The main advantage of emergency mode over single-user mode is that the init files are not loaded. If init is corrupted or not working, you can still mount file systems to recover data that could be lost during a re-installation.

Part II. File Systems

File system refers to the files and directories stored on a computer. A file system can have different formats called file system types. These formats determine how the information is stored as files and directories. Some file system types store redundant copies of the data, while some file system types make hard drive access faster. This part discusses the ext3, swap, RAID, and LVM file system types. It also discusses the parted utility to manage partitions and access control lists (ACLs) to customize file permissions.

Chapter 6. The ext3 File System

6.1. Features of ext3

The ext3 file system is essentially an enhanced version of the ext2 file system. These improvements provide the following advantages:

Availability

After an unexpected power failure or system crash (also called an unclean system shutdown), each mounted ext2 file system on the machine must be checked for consistency by the e2fsck program. This is a time-consuming process that can delay system boot time significantly, especially with large volumes containing a large number of files. During this time, any data on the volumes is unreachable.

The journaling provided by the ext3 file system means that this sort of file system check is no longer necessary after an unclean system shutdown. The only time a consistency check occurs using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to recover an ext3 file system after an unclean system shutdown does not depend on the size of the file system or the number of files; rather, it depends on the size of the journal used to maintain consistency. The default journal size takes about a second to recover, depending on the speed of the hardware.

Data Integrity

The ext3 file system provides stronger data integrity in the event that an unclean system shutdown occurs. The ext3 file system allows you to choose the type and level of protection that your data receives. By default, the ext3 volumes are configured to keep a high level of data consistency with regard to the state of the file system.

Speed

Despite writing some data more than once, ext3 has a higher throughput in most cases than ext2 because ext3's journaling optimizes hard drive head motion. You can choose from three journaling modes to optimize speed, but doing so means trade-offs in regards to data integrity.

6.2. Creating an ext3 File System

After installation, it is sometimes necessary to create a new ext3 file system. For example, if you add a new disk drive to the system, you may want to partition the drive and use the ext3 file system.

The steps for creating an ext3 file system are as follows:

Create the partition using parted or fdisk.

Format the partition with the ext3 file system using mkfs.

Label the partition using e2label.

Create the mount point.

Add the partition to the /etc/fstab file.

6.3. Converting to an ext3 File System

The tune2fs program can add a journal to an existing ext2 file system without altering the data already on the partition. If the file system is already mounted while it is being transitioned, the journal is visible as the file .journal in the root directory of the file system. If the file system is not mounted, the journal is hidden and does not appear in the file system at all.

For the remainder of this section, the sample commands use the following value:

/dev/mapper/VolGroup00-LogVol02

After doing this, be certain to change the partition type from ext2 to ext3 in the /etc/fstab file.

If you are transitioning your root file system, you must use an initrd image (or RAM disk) to boot. To create this, run the mkinitrd program. For information on using the mkinitrd command, type man mkinitrd. Also, make sure your GRUB configuration loads the initrd.

If you fail to make this change, the system still boots, but the file system is mounted as ext2 instead of ext3.

6.4. Reverting to an ext2 File System

Because ext3 is relatively new, some disk utilities do not yet support it. For example, you may need to shrink a partition with resize2fs, which does not yet support ext3. In this situation, it may be necessary to temporarily revert a file system to ext2.

To revert a partition, you must first unmount the partition by logging in as root and typing,

umount /dev/mapper/VolGroup00-LogVol02

Next, change the file system type to ext2 by typing the following command as root:

/sbin/tune2fs -O ^has_journal /dev/mapper/VolGroup00-LogVol02

Check the partition for errors by typing the following command as root:

/sbin/e2fsck -y /dev/mapper/VolGroup00-LogVol02

Then mount the partition again as ext2 file system by typing:

mount -t ext2 /dev/mapper/VolGroup00-LogVol02/mount/point

In the above command, replace /mount/point with the mount point of the partition.

Next, remove the .journal file at the root level of the partition by changing to the directory where it is mounted and typing:

rm -f .journal

You now have an ext2 partition.

If you want to permanently change the partition to ext2, remember to update the /etc/fstab file.

Tip

You can increase the size of an ext3 file system using ext2online. ext2online allows you to increase the size of an ext3 file system once it is mounted (online) and on a resizable logical volume. The root file system is set up by default on LVM2 logical volumes during installation.

Note that ext2online will only work on ext3 file systems. For more information, refer to man ext2online.

Chapter 7. Logical Volume Manager (LVM)

7.1. What is LVM?

LVM is a method of allocating hard drive space into logical volumes that can be easily resized instead of partitions.

With LVM, a hard drive or set of hard drives is allocated to one or more physical volumes. A physical volume cannot span over more than one drive.

The physical volumes are combined into logical volume groups, with the exception of the /boot/ partition. The /boot/ partition cannot be on a logical volume group because the boot loader cannot read it. If the root (/) partition is on a logical volume, create a separate /boot/ partition which is not a part of a volume group.

Since a physical volume cannot span over multiple drives, to span over more than one drive, create one or more physical volumes per drive.

Figure 7.1. Logical Volume Group

The logical volume group is divided into logical volumes, which are assigned mount points, such as /home and / m and file system types, such as ext2 or ext3. When "partitions" reach their full capacity, free space from the logical volume group can be added to the logical volume to increase the size of the partition. When a new hard drive is added to the system, it can be added to the logical volume group, and partitions that are logical volumes can be expanded.

Figure 7.2. Logical Volumes

On the other hand, if a system is partitioned with the ext3 file system, the hard drive is divided into partitions of defined sizes. If a partition becomes full, it is not easy to expand the size of the partition. Even if the partition is moved to another hard drive, the original hard drive space has to be reallocated as a different partition or not used.

LVM support must be compiled into the kernel, and the default Red Hat kernel is compiled with LVM support.

7.2. What is LVM2?

LVM version 2, or LVM2, is the default for Red Hat Enterprise Linux, which uses the device mapper driver contained in the 2.6 kernel. LVM2, which is almost completely compatible with the earlier LVM1 version, can be upgraded from versions of Red Hat Enterprise Linux running the 2.4 kernel.

Although upgrading from LVM1 to LVM2 is usually seamless, refer to Section 7.3, “Additional Resources” for further details on more complex requirements and upgrading scenarios.

7.3. Additional Resources

Use these sources to learn more about LVM.

7.3.1. Installed Documentation

rpm -qd lvm — This command shows all the documentation available from the lvm package, including man pages.

LVM can be configured during the graphical installation process, the text-based installation process, or during a kickstart installation. You can use the utilities from the lvm package to create your own LVM configuration post-installation, but these instructions focus on using Disk Druid during installation to complete this task.

Although the following steps are illustrated during a GUI installation, the same can be done during a text-based installation.

Two 9.1 GB SCSI drives (/dev/sda and /dev/sdb) are used in the following examples. They detail how to create a simple configuration using a single LVM volume group with associated logical volumes during installation.

8.1. Automatic Partitioning

For Red Hat Enterprise Linux, LVM is the default method for disk partitioning. If you do not wish to have LVM implemented, or if you require RAID partitioning, manual disk partitioning through Disk Druid is required.

The following properties make up the automatically created configuration:

The /boot/ partition resides on its own non-LVM partition. In the following example, it is the first partition on the first drive (/dev/sda1). Bootable partitions cannot reside on LVM logical volumes.

A single LVM volume group (VolGroup00) is created, which spans all selected drives and all remaining space available. In the following example, the remainder of the first drive (/dev/sda2), and the entire second drive (/dev/sdb1) are allocated to the volume group.

Two LVM logical volumes (LogVol00 and LogVol01) are created from the newly created spanned volume group. In the following example, the recommended swap space is automatically calculated and assigned to LogVol01, and the remainder is allocated to the root file system, LogVol00.

Figure 8.1. Automatic LVM Configuration With Two SCSI Drives

Note

If enabling quotas are of interest to you, it may be best to modify the automatic configuration to include other mount points, such as /home/ or /var/, so that each file system has its own independent quota configuration limits.

In most cases, the default automatic LVM partitioning is sufficient, but advanced implementations could warrant modification or manual configuration of the LVM partition tables.

Note

If you anticipate future memory upgrades, leaving some free space in the volume group would allow for easy future expansion of the swap space logical volume on the system; in which case, the automatic LVM configuration should be modified to leave available space for future growth.

8.2. Manual LVM Partitioning

The following section explains how to manually configure LVM for Red Hat Enterprise Linux. Because there are numerous ways to manually configure a system with LVM, the following example is similar to the default configuration done in Section 8.1, “Automatic Partitioning”.

The /boot/ partition cannot reside on an LVM volume group because the GRUB boot loader cannot read it.

Select New.

Select /boot from the Mount Point pulldown menu.

Select ext3 from the File System Type pulldown menu.

Select only the sda checkbox from the Allowable Drives area.

Leave 100 (the default) in the Size (MB) menu.

Leave the Fixed size (the default) radio button selected in the Additional Size Options area.

Select Force to be a primary partition to make the partition be a primary partition. A primary partition is one of the first four partitions on the hard drive. If unselected, the partition is created as a logical partition. If other operating systems are already on the system, unselecting this option should be considered. For more information on primary versus logical/extended partitions, refer to the appendix section of the Installation Guide.

Click OK to return to the main screen. The following figure displays the boot partition correctly set:

Figure 8.4. The /boot/ Partition Displayed

8.2.2. Creating the LVM Physical Volumes

Once the boot partition is created, the remainder of all disk space can be allocated to LVM partitions. The first step in creating a successful LVM implementation is the creation of the physical volume(s).

You cannot enter a mount point yet (you can once you have created all your physical volumes and then all volume groups).

A physical volume must be constrained to one drive. For Allowable Drives, select the drive on which the physical volume are created. If you have multiple drives, all drives are selected, and you must deselect all but one drive.

Enter the size that you want the physical volume to be.

Select Fixed size to make the physical volume the specified size, select Fill all space up to (MB) and enter a size in MBs to give range for the physical volume size, or select Fill to maximum allowable size to make it grow to fill all available space on the hard disk. If you make more than one growable, they share the available free space on the disk.

Select Force to be a primary partition if you want the partition to be a primary partition.

Click OK to return to the main screen.

Repeat these steps to create as many physical volumes as needed for your LVM setup. For example, if you want the volume group to span over more than one drive, create a physical volume on each of the drives. The following figure shows both drives completed after the repeated process:

Figure 8.6. Two Physical Volumes Created

8.2.3. Creating the LVM Volume Groups

Once all the physical volumes are created, the volume groups can be created:

Click the LVM button to collect the physical volumes into volume groups. A volume group is basically a collection of physical volumes. You can have multiple logical volume groups, but a physical volume can only be in one volume group.

Note

There is overhead disk space reserved in the logical volume group. The summation of the physical volumes may not equal the size of the volume group; however, the size of the logical volumes shown is correct.

Figure 8.7. Creating an LVM Volume Group

Change the Volume Group Name if desired.

All logical volumes inside the volume group must be allocated in physical extent units. By default, the physical extent is set to 32 MB; thus, logical volume sizes must be divisible by 32 MBs. If you enter a size that is not a unit of 32 MBs, the installation program automatically selects the closest size in units of 32 MBs. It is not recommended that you change this setting.

Select which physical volumes to use for the volume group.

8.2.4. Creating the LVM Logical Volumes

Create logical volumes with mount points such as /, /home/, and swap space. Remember that /boot cannot be a logical volume. To add a logical volume, click the Add button in the Logical Volumes section. A dialog window as shown in Figure 8.8, “Creating a Logical Volume” appears.

Figure 8.8. Creating a Logical Volume

Repeat these steps for each volume group you want to create.

Tip

You may want to leave some free space in the logical volume group so you can expand the logical volumes later. The default automatic configuration does not do this, but this manual configuration example does — approximately 1 GB is left as free space for future expansion.

Figure 8.9. Pending Logical Volumes

Click OK to apply the volume group and all associated logical volumes.

The following figure shows the final manual configuration:

Figure 8.10. Final Manual Configuration

Chapter 9. Redundant Array of Independent Disks (RAID)

9.1. What is RAID?

The basic idea behind RAID is to combine multiple small, inexpensive disk drives into an array to accomplish performance or redundancy goals not attainable with one large and expensive drive. This array of drives appears to the computer as a single logical storage unit or drive.

RAID is a method in which information is spread across several disks. RAID uses techniques such as disk striping (RAID Level 0), disk mirroring (RAID level 1), and disk striping with parity (RAID Level 5) to achieve redundancy, lower latency and/or to increase bandwidth for reading or writing to disks, and to maximize the ability to recover from hard disk crashes.

The underlying concept of RAID is that data may be distributed across each drive in the array in a consistent manner. To do this, the data must first be broken into consistently-sized chunks (often 32K or 64K in size, although different sizes can be used). Each chunk is then written to a hard drive in the RAID array according to the RAID level used. When the data is to be read, the process is reversed, giving the illusion that the multiple drives in the array are actually one large drive.

9.2. Who Should Use RAID?

Those who need to keep large quantities of data on hand (such as system administrators) would benefit by using RAID technology. Primary reasons to use RAID include:

Enhanced speed

Increased storage capacity using a single virtual disk

Lessened impact of a disk failure

9.3. Hardware RAID versus Software RAID

There are two possible RAID approaches: Hardware RAID and Software RAID.

9.3.1. Hardware RAID

The hardware-based array manages the RAID subsystem independently from the host and presents to the host only a single disk per RAID array.

An example of a Hardware RAID device would be one that connects to a SCSI controller and presents the RAID arrays as a single SCSI drive. An external RAID system moves all RAID handling "intelligence" into a controller located in the external disk subsystem. The whole subsystem is connected to the host via a normal SCSI controller and appears to the host as a single disk.

RAID controllers also come in the form of cards that act like a SCSI controller to the operating system but handle all of the actual drive communications themselves. In these cases, you plug the drives into the RAID controller just like you would a SCSI controller, but then you add them to the RAID controller's configuration, and the operating system never knows the difference.

9.3.2. Software RAID

Software RAID implements the various RAID levels in the kernel disk (block device) code. It offers the cheapest possible solution, as expensive disk controller cards or hot-swap chassis [2] are not required. Software RAID also works with cheaper IDE disks as well as SCSI disks. With today's fast CPUs, Software RAID performance can excel against Hardware RAID.

The MD driver in the Linux kernel is an example of a RAID solution that is completely hardware independent. The performance of a software-based array is dependent on the server CPU performance and load.

For those interested in learning more about what Software RAID has to offer, here are the most important features:

Threaded rebuild process

Kernel-based configuration

Portability of arrays between Linux machines without reconstruction

Backgrounded array reconstruction using idle system resources

Hot-swappable drive support

Automatic CPU detection to take advantage of certain CPU optimizations

9.4. RAID Levels and Linear Support

RAID supports various configurations, including levels 0, 1, 4, 5, and linear. These RAID types are defined as follows:

Level 0 — RAID level 0, often called "striping," is a performance-oriented striped data mapping technique. This means the data being written to the array is broken down into strips and written across the member disks of the array, allowing high I/O performance at low inherent cost but provides no redundancy. The storage capacity of a level 0 array is equal to the total capacity of the member disks in a Hardware RAID or the total capacity of member partitions in a Software RAID.

Level 1 — RAID level 1, or "mirroring," has been used longer than any other form of RAID. Level 1 provides redundancy by writing identical data to each member disk of the array, leaving a "mirrored" copy on each disk. Mirroring remains popular due to its simplicity and high level of data availability. Level 1 operates with two or more disks that may use parallel access for high data-transfer rates when reading but more commonly operate independently to provide high I/O transaction rates. Level 1 provides very good data reliability and improves performance for read-intensive applications but at a relatively high cost. [3] The storage capacity of the level 1 array is equal to the capacity of one of the mirrored hard disks in a Hardware RAID or one of the mirrored partitions in a Software RAID.

Level 4 — Level 4 uses parity [4] concentrated on a single disk drive to protect data. It is better suited to transaction I/O rather than large file transfers. Because the dedicated parity disk represents an inherent bottleneck, level 4 is seldom used without accompanying technologies such as write-back caching. Although RAID level 4 is an option in some RAID partitioning schemes, it is not an option allowed in Red Hat Enterprise Linux RAID installations. [5] The storage capacity of Hardware RAID level 4 is equal to the capacity of member disks, minus the capacity of one member disk. The storage capacity of Software RAID level 4 is equal to the capacity of the member partitions, minus the size of one of the partitions if they are of equal size.

Level 5 — This is the most common type of RAID. By distributing parity across some or all of an array's member disk drives, RAID level 5 eliminates the write bottleneck inherent in level 4. The only performance bottleneck is the parity calculation process. With modern CPUs and Software RAID, that usually is not a very big problem. As with level 4, the result is asymmetrical performance, with reads substantially outperforming writes. Level 5 is often used with write-back caching to reduce the asymmetry. The storage capacity of Hardware RAID level 5 is equal to the capacity of member disks, minus the capacity of one member disk. The storage capacity of Software RAID level 5 is equal to the capacity of the member partitions, minus the size of one of the partitions if they are of equal size.

Linear RAID — Linear RAID is a simple grouping of drives to create a larger virtual drive. In linear RAID, the chunks are allocated sequentially from one member drive, going to the next drive only when the first is completely filled. This grouping provides no performance benefit, as it is unlikely that any I/O operations will be split between member drives. Linear RAID also offers no redundancy and, in fact, decreases reliability — if any one member drive fails, the entire array cannot be used. The capacity is the total of all member disks.

[2]
A hot-swap chassis allows you to remove a hard drive without having to power-down your system.

[3]
RAID level 1 comes at a high cost because you write the same information to all of the disks in the array, which wastes drive space. For example, if you have RAID level 1 set up so that your root (/) partition exists on two 40G drives, you have 80G total but are only able to access 40G of that 80G. The other 40G acts like a mirror of the first 40G.

[4]
Parity information is calculated based on the contents of the rest of the member disks in the array. This information can then be used to reconstruct data when one disk in the array fails. The reconstructed data can then be used to satisfy I/O requests to the failed disk before it is replaced and to repopulate the failed disk after it has been replaced.

[5]
RAID level 4 takes up the same amount of space as RAID level 5, but level 5 has more advantages. For this reason, level 4 is not supported.

Chapter 10. Software RAID Configuration

Software RAID can be configured during the graphical installation process, the text-based installation process, or during a kickstart installation. This chapter discusses how to configure software RAID during installation, using the Disk Druid interface.

Choose Create a software RAID partition to create a RAID partition as shown in Figure 10.2, “RAID Partition Options”. Note that no other RAID options (such as entering a mount point) are available until RAID partitions, as well as RAID devices, are created.

Figure 10.2. RAID Partition Options

A software RAID partition must be constrained to one drive. For Allowable Drives, select the drive on which RAID is to be created. If you have multiple drives, all drives are selected, and you must deselect all but one drive.

Figure 10.3. Adding a RAID Partition

Enter the size that you want the partition to be.

Select Fixed size to make the partition the specified size, select Fill all space up to (MB) and enter a size in MBs to give range for the partition size, or select Fill to maximum allowable size to make it grow to fill all available space on the hard disk. If you make more than one partition growable, they share the available free space on the disk.

Select Force to be a primary partition if you want the partition to be a primary partition. A primary partition is one of the first four partitions on the hard drive. If unselected, the partition is created as a logical partition. If other operating systems are already on the system, unselecting this option should be considered. For more information on primary versus logical/extended partitions, refer to the appendix section of the Installation Guide.

Click OK to return to the main screen.

Repeat these steps to create as many partitions as needed for your RAID setup. Notice that all the partitions do not have to be RAID partitions. For example, you can configure only the /boot/ partition as a software RAID device, leaving the root partition (/), /home/, and swap as regular file systems. Figure 10.4, “RAID 1 Partitions Ready, Pre-Device and Mount Point Creation” shows successfully allocated space for the RAID 1 configuration (for /boot/), which is now ready for RAID device and mount point creation:

Choose the file system type for the partition. At this point you can either configure a dynamic LVM file system or a traditional static ext2/ext3 file system. For more information on configuring LVM on a RAID device, select physical volume (LVM) and then refer to Chapter 8, LVM Configuration. If LVM is not required, continue on with the following instructions.

If you are making a RAID partition of /boot/, you must choose RAID level 1, and it must use one of the first two drives (IDE first, SCSI second). If you are not creating a seperate RAID partition of /boot/, and you are making a RAID partition for the root file system (/), it must be RAID level 1 and must use one of the first two drives (IDE first, SCSI second).

Figure 10.7. The /boot/ Mount Error

The RAID partitions created appear in the RAID Members list. Select which of these partitions should be used to create the RAID device.

If configuring RAID 1 or RAID 5, specify the number of spare partitions. If a software RAID partition fails, the spare is automatically used as a replacement. For each spare you want to specify, you must create an additional software RAID partition (in addition to the partitions for the RAID device). Select the partitions for the RAID device and the partition(s) for the spare(s).

After clicking OK, the RAID device appears in the Drive Summary list.

Repeat this chapter's entire process for configuring additional partitions, devices, and mount points, such as the root partition (/), /home/, or swap.

11.1. What is Swap Space?

Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.

Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap partitions and swap files.

The size of your swap should be equal to twice your computer's physical RAM for up to 2 GB of physical RAM. For physical RAM above 2 GB, the size of your swap should be equal to the amount of physical RAM above 2 GB. The size of your swap should never be less than 32 MB.

Using this basic formula, a system with 2 GB of physical RAM would have 4 GB of swap, while one with 3 GB of physical RAM would have 5 GB of swap.

Note

Unfortunately, deciding on the amount of swap to allocate to Red Hat Enterprise Linux is more of an art than a science, so hard rules are not possible. Each system's most used applications should be accounted for when determining swap size.

Important

File systems and LVM2 volumes assigned as swap space cannot be in use when being modified. For example, no system processes can be assigned the swap space, as well as no amount of swap should be allocated and used by the kernel. Use the free and cat /proc/swaps commands to verify how much and where swap is in use.

The best way to achieve swap space modifications is to boot your system in rescue mode, and then follow the instructions (for each scenario) in the remainder of this chapter. Refer to Chapter 5, Basic System Recovery for instructions on booting into rescue mode. When prompted to mount the file system, select Skip.

11.2. Adding Swap Space

Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 128 MB to 256 MB, but there is only 256 MB of swap space. It might be advantageous to increase the amount of swap space to 512 MB if you perform memory-intense operations or run applications that require a large amount of memory.

You have three options: create a new swap partition, create a new swap file, or extend swap on an existing LVM2 logical volume. It is recommended that you extend an existing logical volume.

11.2.1. Extending Swap on an LVM2 Logical Volume

To extend an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):

Disable swapping for the associated logical volume:

# swapoff -v /dev/VolGroup00/LogVol01

Resize the LVM2 logical volume by 256 MB:

# lvm lvresize /dev/VolGroup00/LogVol01 -L +256M

Format the new swap space:

# mkswap /dev/VolGroup00/LogVol01

Enable the extended logical volume:

# swapon -va

Test that the logical volume has been extended properly:

# cat /proc/swaps # free

11.2.2. Creating an LVM2 Logical Volume for Swap

To add a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want to add):

Create the LVM2 logical volume of size 256 MB:

# lvm lvcreate VolGroup00 -n LogVol02 -L 256M

Format the new swap space:

# mkswap /dev/VolGroup00/LogVol02

Add the following entry to the /etc/fstab file:

/dev/VolGroup00/LogVol02 swap swap defaults 0 0

Enable the extended logical volume:

# swapon -va

Test that the logical volume has been extended properly:

# cat /proc/swaps # free

11.2.3. Creating a Swap File

To add a swap file:

Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 64 MB swap file is 65536.

At a shell prompt as root, type the following command with count being equal to the desired block size:

dd if=/dev/zero of=/swapfile bs=1024 count=65536

Setup the swap file with the command:

mkswap /swapfile

To enable the swap file immediately but not automatically at boot time:

swapon /swapfile

To enable it at boot time, edit /etc/fstab to include the following entry:

/swapfile swap swap defaults 0 0

The next time the system boots, it enables the new swap file.

After adding the new swap file and enabling it, verify it is enabled by viewing the output of the command cat /proc/swaps or free.

11.3. Removing Swap Space

Sometimes it can be prudent to reduce swap space after installation. For example, say you downgraded the amount of RAM in your system from 1 GB to 512 MB, but there is 2 GB of swap space still assigned. It might be advantageous to reduce the amount of swap space to 1 GB, since the larger 2 GB could be wasting disk space.

You have three options: remove an entire LVM2 logical volume used for swap, remove a swap file, or reduce swap space on an existing LVM2 logical volume.

11.3.1. Reducing Swap on an LVM2 Logical Volume

To reduce an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):

Disable swapping for the associated logical volume:

# swapoff -v /dev/VolGroup00/LogVol01

Reduce the LVM2 logical volume by 512 MB:

# lvm lvreduce /dev/VolGroup00/LogVol01 -L -512M

Format the new swap space:

# mkswap /dev/VolGroup00/LogVol01

Enable the extended logical volume:

# swapon -va

Test that the logical volume has been reduced properly:

# cat /proc/swaps # free

11.3.2. Removing an LVM2 Logical Volume for Swap

The swap logical volume cannot be in use (no system locks or processes on the volume). The easiest way to achieve this it to boot your system in rescue mode. Refer to Chapter 5, Basic System Recovery for instructions on booting into rescue mode. When prompted to mount the file system, select Skip.

To remove a swap volume group (assuming /dev/VolGroup00/LogVol02 is the swap volume you want to remove):

Disable swapping for the associated logical volume:

# swapoff -v /dev/VolGroup00/LogVol02

Remove the LVM2 logical volume of size 512 MB:

# lvm lvremove /dev/VolGroup00/LogVol02

Remove the following entry from the /etc/fstab file:

/dev/VolGroup00/LogVol02 swap swap defaults 0 0

Test that the logical volume has been extended properly:

# cat /proc/swaps # free

11.3.3. Removing a Swap File

To remove a swap file:

At a shell prompt as root, execute the following command to disable the swap file (where /swapfile is the swap file):

# swapoff -v /swapfile

Remove its entry from the /etc/fstab file.

Remove the actual file:

# rm /swapfile

11.4. Moving Swap Space

To move swap space from one location to another, follow the steps for removing swap space, and then follow the steps for adding swap space.

12.1. Standard Partitions using parted

Many users need to view the existing partition table, change the size of the partitions, remove partitions, or add partitions from free space or additional hard drives. The utility parted allows users to perform these tasks. This chapter discusses how to use parted to perform file system tasks.

You must have the parted package installed to use the parted utility. To start parted, at a shell prompt as root, type the command parted /dev/sda, where /dev/sda is the device name for the drive you want to configure. The (parted) prompt is displayed. Type help to view a list of available commands.

If you want to create, remove, or resize a partition, the device cannot be in use (partitions cannot be mounted, and swap space cannot be enabled). The partition table should not be modified while in use because the kernel may not properly recognize the changes. Data could be overwritten by writing to the wrong partition because the partition table and partitions mounted do not match. The easiest way to achieve this it to boot your system in rescue mode. Refer to Chapter 5, Basic System Recovery for instructions on booting into rescue mode. When prompted to mount the file system, select Skip.

Alternately, if the drive does not contain any partitions in use (system processes that use or lock the file system from being unmounted), you can unmount them with the umount command and turn off all the swap space on the hard drive with the swapoff command.

The first line displays the size of the disk, the second line displays the disk label type, and the remaining output shows the partition table.

In the partition table, the Minor number is the partition number. For example, the partition with minor number 1 corresponds to /dev/sda1. The Start and End values are in megabytes. The Type is one of primary, extended, or logical. The Filesystem is the file system type, which can be one of ext2, ext3, fat16, fat32, hfs, jfs, linux-swap, ntfs, reiserfs, hp-ufs, sun-ufs, or xfs. The Flags column lists the flags set for the partition. Available flags are boot, root, swap, hidden, raid, lvm, or lba.

In this example, minor number 1 refers to the /boot/ file system, minor number 2 refers to the root file system (/), minor number 3 refers to the swap, and minor number 5 refers to the /home/ file system.

Tip

To select a different device without having to restart parted, use the select command followed by the device name such as /dev/sda. Then, you can view its partition table or configure it.

12.1.2. Creating a Partition

Warning

Do not attempt to create a partition on a device that is in use.

Before creating a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to create the partition:

parted /dev/sda

View the current partition table to determine if there is enough free space:

12.1.2.1. Making the Partition

From the partition table, determine the start and end points of the new partition and what partition type it should be. You can only have four primary partitions (with no extended partition) on a device. If you need more than four partitions, you can have three primary partitions, one extended partition, and multiple logical partitions within the extended. For an overview of disk partitions, refer to the appendix An Introduction to Disk Partitions in the Installation Guide.

For example, to create a primary partition with an ext3 file system from 1024 megabytes until 2048 megabytes on a hard drive type the following command:

mkpart primary ext3 1024 2048

Tip

If you use the mkpartfs command instead, the file system is created after the partition is created. However, parted does not support creating an ext3 file system. Thus, if you wish to create an ext3 file system, use mkpart and create the file system with the mkfs command as described later. mkpartfs works for file system type linux-swap.

The changes start taking place as soon as you press Enter, so review the command before executing to it.

After creating the partition, use the print command to confirm that it is in the partition table with the correct partition type, file system type, and size. Also remember the minor number of the new partition so that you can label it. You should also view the output of

cat /proc/partitions

to make sure the kernel recognizes the new partition.

12.1.2.2. Formating the Partition

The partition still does not have a file system. Create the file system:

/sbin/mkfs -t ext3 /dev/sda6

Warning

Formatting the partition permanently destroys any data that currently exists on the partition.

12.1.2.3. Labeling the Partition

Next, give the partition a label. For example, if the new partition is /dev/sda6 and you want to label it /work:

e2label /dev/sda6 /work

By default, the installation program uses the mount point of the partition as the label to make sure the label is unique. You can use any label you want.

12.1.2.4. Creating the Mount Point

As root, create the mount point:

mkdir /work

12.1.2.5. Add to /etc/fstab

As root, edit the /etc/fstab file to include the new partition. The new line should look similar to the following:

LABEL=/work /work ext3 defaults 1 2

The first column should contain LABEL= followed by the label you gave the partition. The second column should contain the mount point for the new partition, and the next column should be the file system type (for example, ext3 or swap). If you need more information about the format, read the man page with the command man fstab.

If the fourth column is the word defaults, the partition is mounted at boot time. To mount the partition without rebooting, as root, type the command:

mount /work

12.1.3. Removing a Partition

Warning

Do not attempt to remove a partition on a device that is in use.

Before removing a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to remove the partition:

parted /dev/sda

View the current partition table to determine the minor number of the partition to remove:

print

Remove the partition with the command rm. For example, to remove the partition with minor number 3:

rm 3

The changes start taking place as soon as you press Enter, so review the command before committing to it.

After removing the partition, use the print command to confirm that it is removed from the partition table. You should also view the output of

cat /proc/partitions

to make sure the kernel knows the partition is removed.

The last step is to remove it from the /etc/fstab file. Find the line that declares the removed partition, and remove it from the file.

12.1.4. Resizing a Partition

Warning

Do not attempt to resize a partition on a device that is in use.

Before resizing a partition, boot into rescue mode (or unmount any partitions on the device and turn off any swap space on the device).

Start parted, where /dev/sda is the device on which to resize the partition:

parted /dev/sda

View the current partition table to determine the minor number of the partition to resize as well as the start and end points for the partition:

print

Warning

The used space of the partition to resize must not be larger than the new size.

To resize the partition, use the resize command followed by the minor number for the partition, the starting place in megabytes, and the end place in megabytes. For example:

resize 3 1024 2048

After resizing the partition, use the print command to confirm that the partition has been resized correctly, is the correct partition type, and is the correct file system type.

After rebooting the system into normal mode, use the command df to make sure the partition was mounted and is recognized with the new size.

12.2. LVM Partition Management

The following commands can be found by issuing lvm help at a command prompt.

Disk space can be restricted by implementing disk quotas which alert a system administrator before a user consumes too much disk space or a partition becomes full.

Disk quotas can be configured for individual users as well as user groups. This kind of flexibility makes it possible to give each user a small quota to handle "personal" files (such as email and reports), while allowing the projects they work on to have more sizable quotas (assuming the projects are given their own groups).

In addition, quotas can be set not just to control the number of disk blocks consumed but to control the number of inodes (data structures that contain information about files in UNIX file systems). Because inodes are used to contain file-related information, this allows control over the number of files that can be created.

The quota RPM must be installed to implement disk quotas.

13.1. Configuring Disk Quotas

To implement disk quotas, use the following steps:

Enable quotas per file system by modifying the /etc/fstab file.

Remount the file system(s).

Create the quota database files and generate the disk usage table.

Assign quota policies.

Each of these steps is discussed in detail in the following sections.

13.1.1. Enabling Quotas

As root, using a text editor, edit the /etc/fstab file. Add the usrquota and/or grpquota options to the file systems that require quotas:

In this example, the /home file system has both user and group quotas enabled.

Note

The following examples assume that a separate /home partition was created during the installation of Red Hat Enterprise Linux. Although not ideal, the root (/) partition (the installation default created partition) can be used for setting quota policies in the /etc/fstab file.

13.1.2. Remounting the File Systems

After adding the usrquota and/or grpquota options, remount each file system whose fstab entry has been modified. If the file system is not in use by any process, use one of the following methods:

Issue the umount command followed by the mount command to remount the file system.

Issue the mount -o remount /home command to remount the file system.

If the file system is currently in use, the easiest method for remounting the file system is to reboot the system.

13.1.3. Creating the Quota Database Files

After each quota-enabled file system is remounted, the system is capable of working with disk quotas. However, the file system itself is not yet ready to support quotas. The next step is to run the quotacheck command.

The quotacheck command examines quota-enabled file systems and builds a table of the current disk usage per file system. The table is then used to update the operating system's copy of disk usage. In addition, the file system's disk quota files are updated.

To create the quota files (aquota.user and aquota.group) on the file system, use the -c option of the quotacheck command. For example, if user and group quotas are enabled for the /home file system, create the files in the /home directory:

quotacheck -cug /home

The -c option specifies that the quota files should be created for each file system with quotas enabled, the -u option specifies to check for user quotas, and the -g option specifies to check for group quotas.

If neither the -u or -g options are specified, only the user quota file is created. If only -g is specified, only the group quota file is created.

After the files are created, run the following command to generate the table of current disk usage per file system with quotas enabled:

quotacheck -avug

The options used are as follows:

a — Check all quota-enabled, locally-mounted file systems

v — Display verbose status information as the quota check proceeds

u — Check user disk quota information

g — Check group disk quota information

After quotacheck has finished running, the quota files corresponding to the enabled quotas (user and/or group) are populated with data for each quota-enabled locally-mounted file system such as /home.

13.1.4. Assigning Quotas per User

The last step is assigning the disk quotas with the edquota command.

To configure the quota for a user, as root in a shell prompt, execute the command:

edquota username

Perform this step for each user who needs a quota. For example, if a quota is enabled in /etc/fstab for the /home partition (/dev/VolGroup00/LogVol02) and the command edquota testuser is executed, the following is shown in the editor configured as the default for the system:

The text editor defined by the EDITOR environment variable is used by edquota. To change the editor, set the EDITOR environment variable in your ~/.bash_profile file to the full path of the editor of your choice.

The first column is the name of the file system that has a quota enabled for it. The second column shows how many blocks the user is currently using. The next two columns are used to set soft and hard block limits for the user on the file system. The inodes column shows how many inodes the user is currently using. The last two columns are used to set the soft and hard inode limits for the user on the file system.

A hard limit is the absolute maximum amount of disk space that a user or group can use. Once this limit is reached, no further disk space can be used.

The soft limit defines the maximum amount of disk space that can be used. However, unlike the hard limit, the soft limit can be exceeded for a certain amount of time. That time is known as the grace period. The grace period can be expressed in seconds, minutes, hours, days, weeks, or months.

If any of the values are set to 0, that limit is not set. In the text editor, change the desired limits. For example:

Change the block grace period or inode grace period, save the changes to the file, and exit the text editor.

13.2. Managing Disk Quotas

If quotas are implemented, they need some maintenance — mostly in the form of watching to see if the quotas are exceeded and making sure the quotas are accurate. Of course, if users repeatedly exceeds their quotas or consistently reaches their soft limits, a system administrator has a few choices to make depending on what type of users they are and how much disk space impacts their work. The administrator can either help the user determine how to use less disk space or increase the user's disk quota if needed.

13.2.1. Enabling and Disabling

It is possible to disable quotas without setting them to be 0. To turn all user and group quotas off, use the following command:

quotaoff -vaug

If neither the -u or -g options are specified, only the user quotas are disabled. If only -g is specified, only group quotas are disabled.

To enable quotas again, use the quotaon command with the same options.

For example, to enable user and group quotas for all file systems, use the following command:

quotaon -vaug

To enable quotas for a specific file system, such as /home, use the following command:

quotaon -vug /home

If neither the -u or -g options are specified, only the user quotas are enabled. If only -g is specified, only group quotas are enabled.

To view the disk usage report for all (option -a) quota-enabled file systems, use the command:

repquota -a

While the report is easy to read, a few points should be explained. The -- displayed after each user is a quick way to determine whether the block or inode limits have been exceeded. If either soft limit is exceeded, a + appears in place of the corresponding -; the first - represents the block limit, and the second represents the inode limit.

The grace columns are normally blank. If a soft limit has been exceeded, the column contains a time specification equal to the amount of time remaining on the grace period. If the grace period has expired, none appears in its place.

13.2.3. Keeping Quotas Accurate

Whenever a file system is not unmounted cleanly (due to a system crash, for example), it is necessary to run quotacheck. However, quotacheck can be run on a regular basis, even if the system has not crashed. Running the following command periodically keeps the quotas more accurate (the options used have been described in Section 13.1.1, “Enabling Quotas”):

quotacheck -avug

The easiest way to run it periodically is to use cron. As root, either use the crontab -e command to schedule a periodic quotacheck or place a script that runs quotacheck in any one of the following directories (using whichever interval best matches your needs):

/etc/cron.hourly

/etc/cron.daily

/etc/cron.weekly

/etc/cron.monthly

The most accurate quota statistics can be obtained when the file system(s) analyzed are not in active use. Thus, the cron task should be schedule during a time where the file system(s) are used the least. If this time is various for different file systems with quotas, run quotacheck for each file system at different times with multiple cron tasks.

13.3. Additional Resources

13.3.1. Installed Documentation

13.3.2. Related Books

Introduction to System Administration ; Red Hat, Inc — Available at http://www.redhat.com/docs/ and on the Documentation CD, this manual contains background information on storage management (including disk quotas) for new Red Hat Enterprise Linux system administrators.

Files and directories have permission sets for the owner of the file, the group associated with the file, and all other users for the system. However, these permission sets have limitations. For example, different permissions cannot be configured for different users. Thus, Access Control Lists (ACLs) were implemented.

The Red Hat Enterprise Linux 4 kernel provides ACL support for the ext3 file system and NFS-exported file systems. ACLs are also recognized on ext3 file systems accessed via Samba.

Along with support in the kernel, the acl package is required to implement ACLs. It contains the utilities used to add, modify, remove, and retrieve ACL information.

The cp and mv commands copy or move any ACLs associated with files and directories.

14.1. Mounting File Systems

Before using ACLs for a file or directory, the partition for the file or directory must be mounted with ACL support. If it is a local ext3 file system, it can mounted with the following command:

mount -t ext3 -o acl <device-name><partition>

For example:

mount -t ext3 -o acl /dev/VolGroup00/LogVol02 /work

Alternatively, if the partition is listed in the /etc/fstab file, the entry for the partition can include the acl option:

LABEL=/work /work ext3 acl 1 2

If an ext3 file system is accessed via Samba and ACLs have been enabled for it, the ACLs are recognized because Samba has been compiled with the --with-acl-support option. No special flags are required when accessing or mounting a Samba share.

14.1.1. NFS

By default, if the file system being exported by an NFS server supports ACLs and the NFS client can read ACLs, ACLs are utilized by the client system.

To disable ACLs on NFS shares when configuring the server, include the no_acl option in the /etc/exports file. To disable ACLs on an NFS share when mounting it on a client, mount it with the no_acl option via the command line or the /etc/fstab file.

14.2. Setting Access ACLs

There are two types of ACLs: access ACLs and default ACLs. An access ACL is the access control list for a specific file or directory. A default ACL can only be associated with a directory; if a file within the directory does not have an access ACL, it uses the rules of the default ACL for the directory. Default ACLs are optional.

ACLs can be configured:

Per user

Per group

Via the effective rights mask

For users not in the user group for the file

The setfacl utility sets ACLs for files and directories. Use the -m option to add or modify the ACL of a file or directory:

setfacl -m <rules><files>

Rules (<rules>) must be specified in the following formats. Multiple rules can be specified in the same command if they are separated by commas.

u:<uid>:<perms>

Sets the access ACL for a user. The user name or UID may be specified. The user may be any valid user on the system.

g:<gid>:<perms>

Sets the access ACL for a group. The group name or GID may be specified. The group may be any valid group on the system.

m:<perms>

Sets the effective rights mask. The mask is the union of all permissions of the owning group and all of the user and group entries.

o:<perms>

Sets the access ACL for users other than the ones in the group for the file.

White space is ignored. Permissions (<perms>) must be a combination of the characters r, w, and x for read, write, and execute.

If a file or directory already has an ACL, and the setfacl command is used, the additional rules are added to the existing ACL or the existing rule is modified.

For example, to give read and write permissions to user andrius:

setfacl -m u:andrius:rw /project/somefile

To remove all the permissions for a user, group, or others, use the -x option and do not specify any permissions:

setfacl -x <rules><files>

For example, to remove all permissions from the user with UID 500:

setfacl -x u:500 /project/somefile

14.3. Setting Default ACLs

To set a default ACL, add d: before the rule and specify a directory instead of a file name.

For example, to set the default ACL for the /share/ directory to read and execute for users not in the user group (an access ACL for an individual file can override it):

setfacl -m d:o:rx /share

14.4. Retrieving ACLs

To determine the existing ACLs for a file or directory, use the getfacl command:

14.5. Archiving File Systems With ACLs

Warning

The tar and dump commands do not backup ACLs.

The star utility is similar to the tar utility in that it can be used to generate archives of files; however, some of its options are different. Refer to Table 14.1, “Command Line Options for star” for a listing of more commonly used options. For all available options, refer to the star man page. The star package is required to use this utility.

Table 14.1. Command Line Options for star

Option

Description

-c

Creates an archive file.

-n

Do not extract the files; use in conjunction with -x to show what extracting the files does.

-r

Replaces files in the archive. The files are written to the end of the archive file, replacing any files with the same path and file name.

-t

Displays the contents of the archive file.

-u

Updates the archive file. The files are written to the end of the archive if they do not exist in the archive or if the files are newer than the files of the same name in the archive. This option only work if the archive is a file or an unblocked tape that may backspace.

-x

Extracts the files from the archive. If used with -U and a file in the archive is older than the corresponding file on the file system, the file is not extracted.

-help

Displays the most important options.

-xhelp

Displays the least important options.

-/

Do not strip leading slashes from file names when extracting the files from an archive. By default, they are striped when files are extracted.

-acl

When creating or extracting, archive or restore any ACLs associated with the files and directories.

14.6. Compatibility with Older Systems

If an ACL has been set on any file on a given file system, that file system has the ext_attr attribute. This attribute can be seen using the following command:

tune2fs -l <filesystem-device>

A file system that has acquired the ext_attr attribute can be mounted with older kernels, but those kernels do not enforce any ACLs which have been set.

Versions of the e2fsck utility included in version 1.22 and higher of the e2fsprogs package (including the versions in Red Hat Enterprise Linux 2.1 and 4) can check a file system with the ext_attr attribute. Older versions refuse to check it.

14.7. Additional Resources

Refer to the follow resources for more information.

14.7.1. Installed Documentation

acl man page — Description of ACLs

getfacl man page — Discusses how to get file access control lists

setfacl man page — Explains how to set file access control lists

star man page — Explains more about the star utility and its many options

14.7.2. Useful Websites

Part III. Package Management

All software on a Red Hat Enterprise Linux system is divided into RPM packages which can be installed, upgraded, or removed. This part describes how to manage the RPM packages on a Red Hat Enterprise Linux system using graphical and command line tools.

The RPM Package Manager (RPM) is an open packaging system, available for anyone to use, which runs on Red Hat Enterprise Linux as well as other Linux and UNIX systems. Red Hat, Inc encourages other vendors to use RPM for their own products. RPM is distributable under the terms of the GPL.

For the end user, RPM makes system updates easy. Installing, uninstalling, and upgrading RPM packages can be accomplished with short commands. RPM maintains a database of installed packages and their files, so you can invoke powerful queries and verifications on your system. If you prefer a graphical interface, you can use the Package Management Tool to perform many RPM commands.

During upgrades, RPM handles configuration files carefully, so that you never lose your customizations — something that you cannot accomplish with regular .tar.gz files.

For the developer, RPM allows you to take software source code and package it into source and binary packages for end users. This process is quite simple and is driven from a single file and optional patches that you create. This clear delineation between pristine sources and your patches along with build instructions eases the maintenance of the package as new versions of the software are released.

Note

Because RPM makes changes to your system, you must be root to install, remove, or upgrade an RPM package.

15.1. RPM Design Goals

To understand how to use RPM, it can be helpful to understand RPM's design goals:

Upgradability

Using RPM, you can upgrade individual components of your system without completely reinstalling. When you get a new release of an operating system based on RPM (such as Red Hat Enterprise Linux), you do not need to reinstall on your machine (as you do with operating systems based on other packaging systems). RPM allows intelligent, fully-automated, in-place upgrades of your system. Configuration files in packages are preserved across upgrades, so you do not lose your customizations. There are no special upgrade files needed to upgrade a package because the same RPM file is used to install and upgrade the package on your system.

Powerful Querying

RPM is designed to provide powerful querying options. You can do searches through your entire database for packages or just for certain files. You can also easily find out what package a file belongs to and from where the package came. The files an RPM package contains are in a compressed archive, with a custom binary header containing useful information about the package and its contents, allowing you to query individual packages quickly and easily.

System Verification

Another powerful feature is the ability to verify packages. If you are worried that you deleted an important file for some package, verify the package. You are notified of any anomalies. At that point, you can reinstall the package if necessary. Any configuration files that you modified are preserved during reinstallation.

Pristine Sources

A crucial design goal was to allow the use of "pristine" software sources, as distributed by the original authors of the software. With RPM, you have the pristine sources along with any patches that were used, plus complete build instructions. This is an important advantage for several reasons. For instance, if a new version of a program comes out, you do not necessarily have to start from scratch to get it to compile. You can look at the patch to see what you might need to do. All the compiled-in defaults, and all of the changes that were made to get the software to build properly, are easily visible using this technique.

The goal of keeping sources pristine may only seem important for developers, but it results in higher quality software for end users, too.

15.2. Using RPM

RPM has five basic modes of operation (not counting package building): installing, uninstalling, upgrading, querying, and verifying. This section contains an overview of each mode. For complete details and options, try rpm --help or refer to Section 15.5, “Additional Resources” for more information on RPM.

15.2.1. Finding RPM Packages

Before using an RPM, you must know where to find them. An Internet search returns many RPM repositories, but if you are looking for RPM packages built by Red Hat, Inc, they can be found at the following locations:

15.2.2. Installing

RPM packages typically have file names like foo-1.0-1.i386.rpm. The file name includes the package name (foo), version (1.0), release (1), and architecture (i386). To install a package, log in as root and type the following command at a shell prompt:

As you can see, RPM prints out the name of the package and then prints a succession of hash marks as the package is installed as a progress meter.

The signature of a package is checked automatically when installing or upgrading a package. The signature confirms that the package was signed by an authorized party. For example, if the verification of the signature fails, an error message such as the following is displayed:

error: V3 DSA signature: BAD, key ID 0352860f

If it is a new, header-only, signature, an error message such as the following is displayed:

error: Header V3 DSA signature: BAD, key ID 0352860f

If you do not have the appropriate key installed to verify the signature, the message contains the word NOKEY such as:

15.2.2.3. Unresolved Dependency

RPM packages can, essentially, depend on other packages, which means that they require other packages to be installed to run properly. If you try to install a package which has an unresolved dependency, output similar to the following is displayed:

If you are installing a package from the Red Hat Enterprise Linux CD-ROM set, it usually suggest the package(s) needed to resolve the dependency. Find the suggested package(s) on the Red Hat Enterprise Linux CD-ROMs or from the Red Hat FTP site (or mirror), and add it to the command:

rpm -ivh foo-1.0-1.i386.rpm bar-2.0.20-3.i386.rpm

If installation of both packages is successful, output similar to the following is displayed:

If it does not suggest a package to resolve the dependency, you can try the --redhatprovides option to determine which package contains the required file. You need the rpmdb-redhat package installed to use this option.

rpm -q --redhatprovides bar.so.2

If the package that contains bar.so.2 is in the installed database from the rpmdb-redhat package, the name of the package is displayed:

bar-2.0.20-3.i386.rpm

To force the installation anyway (which is not recommended since the package may not run correctly), use the --nodeps option.

15.2.3. Uninstalling

Uninstalling a package is just as simple as installing one. Type the following command at a shell prompt:

rpm -e foo

Note

Notice that we used the package namefoo, not the name of the original package filefoo-1.0-1.i386.rpm. To uninstall a package, replace foo with the actual package name of the original package.

You can encounter a dependency error when uninstalling a package if another installed package depends on the one you are trying to remove. For example:

To cause RPM to ignore this error and uninstall the package anyway, which may break the package depending on it, use the --nodeps option.

15.2.4. Upgrading

Upgrading a package is similar to installing one. Type the following command at a shell prompt:

rpm -Uvh foo-2.0-1.i386.rpm

As part of upgrading a package, RPM automatically uninstalls any old versions of the foo package. In fact, you may want to always use -U to install packages which works even when there are no previous versions of the package installed.

Tip

You don't want to use the -U option for installing kernel packages because RPM replaces the previous kernel package. This does not affect a running system, but if the new kernel is unable to boot during your next restart, there would be no other kernel to boot instead.

Because RPM performs intelligent upgrading of packages with configuration files, you may see a message like the following:

saving /etc/foo.conf as /etc/foo.conf.rpmsave

This message means that your changes to the configuration file may not be forward compatible with the new configuration file in the package, so RPM saved your original file and installed a new one. You should investigate the differences between the two configuration files and resolve them as soon as possible, to ensure that your system continues to function properly.

Upgrading is really a combination of uninstalling and installing, so during an RPM upgrade you can encounter uninstalling and installing errors, plus one more. If RPM thinks you are trying to upgrade to a package with an older version number, the output is similar to the following:

package foo-2.0-1 (which is newer than foo-1.0-1) is already installed

To force RPM to upgrade anyway, use the --oldpackage option:

rpm -Uvh --oldpackage foo-1.0-1.i386.rpm

15.2.5. Freshening

Freshening a package is similar to upgrading one. Type the following command at a shell prompt:

rpm -Fvh foo-1.2-1.i386.rpm

RPM's freshen option checks the versions of the packages specified on the command line against the versions of packages that have already been installed on your system. When a newer version of an already-installed package is processed by RPM's freshen option, it is upgraded to the newer version. However, RPM's freshen option does not install a package if no previously-installed package of the same name exists. This differs from RPM's upgrade option, as an upgrade does install packages, whether or not an older version of the package was already installed.

RPM's freshen option works for single packages or package groups. If you have just downloaded a large number of different packages, and you only want to upgrade those packages that are already installed on your system, freshening does the job. If you use freshening, you do not have to delete any unwanted packages from the group that you downloaded before using RPM.

In this case, issue the following command:

rpm -Fvh *.rpm

RPM automatically upgrades only those packages that are already installed.

15.2.6. Querying

Use the rpm -q command to query the database of installed packages. The rpm -q foo command displays the package name, version, and release number of the installed package foo:

foo-2.0-1

Note

To query a package, replace foo with the actual package name.

Instead of specifying the package name, use the following options with -q to specify the package(s) you want to query. These are called Package Selection Options.

-a queries all currently installed packages.

-f <file> queries the package which owns <file>. When specifying a file, you must specify the full path of the file (for example, /bin/ls).

-p <packagefile> queries the package <packagefile>.

There are a number of ways to specify what information to display about queried packages. The following options are used to select the type of information for which you are searching. These are called Information Query Options.

-c displays a list of files marked as configuration files. These are the files you change after installation to adapt the package to your system (for example, sendmail.cf, passwd, inittab, etc.).

For the options that display lists of files, add -v to the command to display the lists in a familiar ls -l format.

15.2.7. Verifying

Verifying a package compares information about files installed from a package with the same information from the original package. Among other things, verifying compares the size, MD5 sum, permissions, type, owner, and group of each file.

The command rpm -V verifies a package. You can use any of the Package Verify Options listed for querying to specify the packages you wish to verify. A simple use of verifying is rpm -V foo, which verifies that all the files in the foo package are as they were when they were originally installed. For example:

To verify a package containing a particular file:

rpm -Vf /usr/bin/vim

To verify ALL installed packages:

rpm -Va

To verify an installed package against an RPM package file:

rpm -Vp foo-1.0-1.i386.rpm

This command can be useful if you suspect that your RPM databases are corrupt.

If everything verified properly, there is no output. If there are any discrepancies, they are displayed. The format of the output is a string of eight characters (a c denotes a configuration file) and then the file name. Each of the eight characters denotes the result of a comparison of one attribute of the file to the value of that attribute recorded in the RPM database. A single period (.) means the test passed. The following characters denote failure of certain tests:

5 — MD5 checksum

S — file size

L — symbolic link

T — file modification time

D — device

U — user

G — group

M — mode (includes permissions and file type)

? — unreadable file

If you see any output, use your best judgment to determine if you should remove or reinstall the package, or fix the problem in another way.

15.3. Checking a Package's Signature

If you wish to verify that a package has not been corrupted or tampered with, examine only the md5sum by typing the following command at a shell prompt (<rpm-file> with file name of the RPM package):

rpm -K --nosignature <rpm-file>

The message <rpm-file>: md5 OK is displayed. This brief message means that the file was not corrupted by the download. To see a more verbose message, replace -K with -Kvv in the command.

On the other hand, how trustworthy is the developer who created the package? If the package is signed with the developer's GnuPG key, you know that the developer really is who they say they are.

An RPM package can be signed using Gnu Privacy Guard (or GnuPG), to help you make certain your downloaded package is trustworthy.

GnuPG is a tool for secure communication; it is a complete and free replacement for the encryption technology of PGP, an electronic privacy program. With GnuPG, you can authenticate the validity of documents and encrypt/decrypt data to and from other recipients. GnuPG is capable of decrypting and verifying PGP 5.x files as well.

During installation, GnuPG is installed by default. That way you can immediately start using GnuPG to verify any packages that you receive from Red Hat. First, you must import Red Hat's public key.

15.3.1. Importing Keys

To verify Red Hat packages, you must import the Red Hat GPG key. To do so, execute the following command at a shell prompt:

rpm --import /usr/share/rhn/RPM-GPG-KEY

To display a list of all keys installed for RPM verification, execute the command:

rpm -qa gpg-pubkey*

For the Red Hat key, the output includes:

gpg-pubkey-db42a60e-37ea5438

To display details about a specific key, use rpm -qi followed by the output from the previous command:

rpm -qi gpg-pubkey-db42a60e-37ea5438

15.3.2. Verifying Signature of Packages

To check the GnuPG signature of an RPM file after importing the builder's GnuPG key, use the following command (replace <rpm-file> with filename of the RPM package):

rpm -K <rpm-file>

If all goes well, the following message is displayed: md5 gpg OK. That means that the signature of the package has been verified and that it is not corrupt.

15.4. Impressing Your Friends with RPM

RPM is a useful tool for both managing your system and diagnosing and fixing problems. The best way to make sense of all of its options is to look at some examples.

Perhaps you have deleted some files by accident, but you are not sure what you deleted. To verify your entire system and see what might be missing, you could try the following command:

rpm -Va

If some files are missing or appear to have been corrupted, you should probably either re-install the package or uninstall and then re-install the package.

At some point, you might see a file that you do not recognize. To find out which package owns it, enter:

rpm -qf /usr/bin/ggv

The output would look like the following:

ggv-2.6.0-2

We can combine the above two examples in the following scenario. Say you are having problems with /usr/bin/paste. You would like to verify the package that owns that program, but you do not know which package owns paste. Enter the following command,

rpm -Vf /usr/bin/paste

and the appropriate package is verified.

Do you want to find out more information about a particular program? You can try the following command to locate the documentation which came with the package that owns that program:

15.5.3. Related Books

Red Hat RPM Guide by Eric Foster-Johnson; Wiley, John &Sons, Incorporated — This book is a comprehensive guide to RPM, from installing package to building RPMs.

Chapter 16. Red Hat Network

Red Hat Network is an Internet solution for managing one or more Red Hat Enterprise Linux systems. All Security Alerts, Bug Fix Alerts, and Enhancement Alerts (collectively known as Errata Alerts) can be downloaded directly from Red Hat using the Package Updater standalone application or through the RHN website available at https://rhn.redhat.com/.

Figure 16.1. Your RHN

Red Hat Network saves you time because you receive email when updated packages are released. You do not have to search the Web for updated packages or security alerts. By default, Red Hat Network installs the packages as well. You do not have to learn how to use RPM or worry about resolving software package dependencies; RHN does it all.

Red Hat Network features include:

Errata Alerts — learn when Security Alerts, Bug Fix Alerts, and Enhancement Alerts are issued for all the systems in your network

You must activate your Red Hat Enterprise Linux product before registering your system with Red Hat Network to make sure your system is entitled to the correct services. To activate your product, go to:

After activating your product, register it with Red Hat Network to receive Errata Updates. The registration process gathers information about the system that is required to notify you of updates. For example, a list of packages installed on the system is compiled so you are only notified about updates that are relevant to your system.

The first time the system is booted, the Software Update Setup Assistant prompts you to register. If you did not register then, select Applications (the main menu on the panel) => System Tools => Package Updater on your desktop to start the registration process. Alternately, execute the command yum update from a shell prompt.

Figure 16.3. Registering with RHN

After registering, use one of the following methods to start receiving updates:

Select Applications (the main menu on the panel) => System Tools => Package Updater on your desktop

Red Hat Enterprise Linux includes a convenient panel icon that displays visible alerts when there is an update for your Red Hat Enterprise Linux system. This panel icon is not present if no updates are available.

Part IV. Network-Related Configuration

After explaining how to configure the network, this part discusses topics related to networking such as how to allow remote logins, share files and directories over the network, and set up a Web server.

To communicate with each other, computers must have a network connection. This is accomplished by having the operating system recognize an interface card (such as Ethernet, ISDN modem, or token ring) and configuring the interface to connect to the network.

The Network Administration Tool can be used to configure the following types of network interfaces:

Ethernet

ISDN

modem

xDSL

token ring

CIPE

wireless devices

It can also be used to configure IPsec connections, manage DNS settings, and manage the /etc/hosts file used to store additional hostnames and IP address combinations.

To use the Network Administration Tool, you must have root privileges. To start the application, go to the Applications (the main menu on the
panel) => System Settings => Network, or type the command system-config-network at a shell prompt (for example, in an XTerm or a GNOME terminal). If you type the command, the graphical version is displayed if X is running; otherwise, the text-based version is displayed.

To use the command line version, execute the command system-config-network-cmd --help as root to view all of the options.

17.1. Overview

To configure a network connection with the Network Administration Tool, perform the following steps:

Add a network device associated with the physical hardware device.

Add the physical hardware device to the hardware list, if it does not already exist.

Configure the hostname and DNS settings.

Configure any hosts that cannot be looked up through DNS.

This chapter discusses each of these steps for each type of network connection.

17.2. Establishing an Ethernet Connection

To establish an Ethernet connection, you need a network interface card (NIC), a network cable (usually a CAT5 cable), and a network to connect to. Different networks are configured to use different network speeds; make sure your NIC is compatible with the network to which you want to connect.

If you have already added the network interface card to the hardware list, select it from the Ethernet card list. Otherwise, select Other Ethernet Card to add the hardware device.

Note

The installation program detects supported Ethernet devices and prompts you to configure them. If you configured any Ethernet devices during the installation, they are displayed in the hardware list on the Hardware tab.

If you selected Other Ethernet Card, the Select Ethernet Adapter window appears. Select the manufacturer and model of the Ethernet card. Select the device name. If this is the system's first Ethernet card, select eth0 as the device name; if this is the second Ethernet card, select eth1 (and so on). The Network Administration Tool also allows you to configure the resources for the NIC. Click Forward to continue.

In the Configure Network Settings window shown in Figure 17.2, “Ethernet Settings”, choose between DHCP and a static IP address. If the device receives a different IP address each time the network is started, do not specify a hostname. Click Forward to continue.

After adding the Ethernet device, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, when the device is added, it is configured to start at boot time by default. To change this setting, select to edit the device, modify the Activate device when computer starts value, and save the changes.

If you associate more than one device with an Ethernet card, the subsequent devices are device aliases. A device alias allows you to setup multiple virtual devices for one physical device, thus giving the one physical device more than one IP address. For example, you can configure an eth1 device and an eth1:1 device. For details, refer to Section 17.11, “Device Aliases”.

17.3. Establishing an ISDN Connection

An ISDN connection is an Internet connection established with a ISDN modem card through a special phone line installed by the phone company. ISDN connections are popular in Europe.

To add an ISDN connection, follow these steps:

Click the Devices tab.

Click the New button on the toolbar.

Select ISDN connection from the Device Type list, and click Forward.

Select the ISDN adapter from the pulldown menu. Then configure the resources and D channel protocol for the adapter. Click Forward to continue.

Figure 17.4. ISDN Settings

If your Internet Service Provider (ISP) is in the pre-configured list, select it. Otherwise, enter the required information about your ISP account. If you do not know the values, contact your ISP. Click Forward.

In the IP Settings window, select the Encapsulation Mode and whether to obtain an IP address automatically or to set a static IP instead. Click Forward when finished.

On the Create Dialup Connection page, click Apply.

After configuring the ISDN device, it appears in the device list as a device with type ISDN as shown in Figure 17.5, “ISDN Device”.

Be sure to select File => Save to save the changes.

After adding the ISDN device, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, when the device is added, it is configured not to start at boot time by default. Edit its configuration to modify this setting. Compression, PPP options, login name, password, and more can be changed.

When the device is added, it is not activated immediately, as seen by its Inactive status. To activate the device, select it from the device list, and click the Activate button. If the system is configured to activate the device when the computer starts (the default), this step does not have to be performed again.

Figure 17.5. ISDN Device

17.4. Establishing a Modem Connection

A modem can be used to configure an Internet connection over an active phone line. An Internet Service Provider (ISP) account (also called a dial-up account) is required.

To add a modem connection, follow these steps:

Click the Devices tab.

Click the New button on the toolbar.

Select Modem connection from the Device Type list, and click Forward.

If there is a modem already configured in the hardware list (on the Hardware tab), the Network Administration Tool assumes you want to use it to establish a modem connection. If there are no modems already configured, it tries to detect any modems in the system. This probe might take a while. If a modem is not found, a message is displayed to warn you that the settings shown are not values found from the probe.

Configure the modem device, baud rate, flow control, and modem volume. If you do not know these values, accept the defaults if the modem was probed successfully. If you do not have touch tone dialing, uncheck the corresponding checkbox. Click Forward.

If your ISP is in the pre-configured list, select it. Otherwise, enter the required information about your ISP account. If you do not know these values, contact your ISP. Click Forward.

On the IP Settings page, select whether to obtain an IP address automatically or whether to set one statically. Click Forward when finished.

After adding the modem device, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, when the device is added, it is configured not to start at boot time by default. Edit its configuration to modify this setting. Compression, PPP options, login name, password, and more can also be changed.

When the device is added, it is not activated immediately, as seen by its Inactive status. To activate the device, select it from the device list, and click the Activate button. If the system is configured to activate the device when the computer starts (the default), this step does not have to be performed again.

17.5. Establishing an xDSL Connection

DSL stands for Digital Subscriber Lines. There are different types of DSL such as ADSL, IDSL, and SDSL. The Network Administration Tool uses the term xDSL to mean all types of DSL connections.

Some DSL providers require that the system is configured to obtain an IP address through DHCP with an Ethernet card. Some DSL providers require you to configure a PPPoE (Point-to-Point Protocol over Ethernet) connection with an Ethernet card. Ask your DSL provider which method to use.

If your Ethernet card is in the hardware list, select the Ethernet Device from the pulldown menu from the page shown in Figure 17.8, “xDSL Settings”. Otherwise, the Select Ethernet Adapter window appears.

Note

The installation program detects supported Ethernet devices and prompts you to configure them. If you configured any Ethernet devices during the installation, they are displayed in the hardware list on the Hardware tab.

Figure 17.8. xDSL Settings

If the Select Ethernet Adapter window appears, select the manufacturer and model of the Ethernet card. Select the device name. If this is the system's first Ethernet card, select eth0 as the device name; if this is the second Ethernet card, select eth1 (and so on). The Network Administration Tool also allows you to configure the resources for the NIC. Click Forward to continue.

Enter the Provider Name, Login Name, and Password. If you have a T-Online account, instead of entering a Login Name and Password in the default window, click the T-Online Account Setup button and enter the required information. Click Forward to continue.

After adding the xDSL connection, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, when the device is added, it is configured not to start at boot time by default. Edit its configuration to modify this setting.

When the device is added, it is not activated immediately, as seen by its Inactive status. To activate the device, select it from the device list, and click the Activate button. If the system is configured to activate the device when the computer starts (the default), this step does not have to be performed again.

17.6. Establishing a Token Ring Connection

A token ring network is a network in which all the computers are connected in a circular pattern. A token, or a special network packet, travels around the token ring and allows computers to send information to each other.

Tip

For more information on using token rings under Linux, refer to the Linux Token Ring Project website available at http://www.linuxtr.net/.

If you have already added the token ring card to the hardware list, select it from the Tokenring card list. Otherwise, select Other Tokenring Card to add the hardware device.

If you selected Other Tokenring Card, the Select Token Ring Adapter window as shown in Figure 17.10, “Token Ring Settings” appears. Select the manufacturer and model of the adapter. Select the device name. If this is the system's first token ring card, select tr0; if this is the second token ring card, select tr1 (and so on). The Network Administration Tool also allows the user to configure the resources for the adapter. Click Forward to continue.

Figure 17.10. Token Ring Settings

On the Configure Network Settings page, choose between DHCP and static IP address. You may specify a hostname for the device. If the device receives a dynamic IP address each time the network is started, do not specify a hostname. Click Forward to continue.

After adding the device, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, you can configure whether the device is started at boot time.

When the device is added, it is not activated immediately, as seen by its Inactive status. To activate the device, select it from the device list, and click the Activate button. If the system is configured to activate the device when the computer starts (the default), this step does not have to be performed again.

17.7. Establishing a Wireless Connection

Wireless Ethernet devices are becoming increasingly popular. The configuration is similar to the Ethernet configuration except that it allows you to configure settings such as the SSID and key for the wireless device.

If you have already added the wireless network interface card to the hardware list, select it from the Wireless card list. Otherwise, select Other Wireless Card to add the hardware device.

Note

The installation program usually detects supported wireless Ethernet devices and prompts you to configure them. If you configured them during the installation, they are displayed in the hardware list on the Hardware tab.

If you selected Other Wireless Card, the Select Ethernet Adapter window appears. Select the manufacturer and model of the Ethernet card and the device. If this is the first Ethernet card for the system, select eth0; if this is the second Ethernet card for the system, select eth1 (and so on). The Network Administration Tool also allows the user to configure the resources for the wireless network interface card. Click Forward to continue.

On the Configure Network Settings page, choose between DHCP and static IP address. You may specify a hostname for the device. If the device receives a dynamic IP address each time the network is started, do not specify a hostname. Click Forward to continue.

After adding the wireless device, you can edit its configuration by selecting the device from the device list and clicking Edit. For example, you can configure the device to activate at boot time.

When the device is added, it is not activated immediately, as seen by its Inactive status. To activate the device, select it from the device list, and click the Activate button. If the system is configured to activate the device when the computer starts (the default), this step does not have to be performed again.

17.8. Managing DNS Settings

The DNS tab allows you to configure the system's hostname, domain, name servers, and search domain. Name servers are used to look up other hosts on the network.

If the DNS server names are retrieved from DHCP or PPPoE (or retrieved from the ISP), do not add primary, secondary, or tertiary DNS servers.

If the hostname is retrieved dynamically from DHCP or PPPoE (or retrieved from the ISP), do not change it.

Figure 17.14. DNS Configuration

Note

The name servers section does not configure the system to be a name server. Instead, it configures which name servers to use when resolving IP addresses to hostnames and vice-versa.

Warning

If the hostname is changed and system-config-network is started on the local host, you may not be able to start another X11 application. As such, you may have to re-login to a new desktop session.

17.9. Managing Hosts

The Hosts tab allows you to add, edit, or remove hosts from the /etc/hosts file. This file contains IP addresses and their corresponding hostnames.

When your system tries to resolve a hostname to an IP address or tries to determine the hostname for an IP address, it refers to the /etc/hosts file before using the name servers (if you are using the default Red Hat Enterprise Linux configuration). If the IP address is listed in the /etc/hosts file, the name servers are not used. If your network contains computers whose IP addresses are not listed in DNS, it is recommended that you add them to the /etc/hosts file.

To add an entry to the /etc/hosts file, go to the Hosts tab, click the New button on the toolbar, provide the requested information, and click OK. Select File => Save or press Ctrl+S to save the changes to the /etc/hosts file. The network or network services do not need to be restarted since the current version of the file is referred to each time an address is resolved.

Warning

Do not remove the localhost entry. Even if the system does not have a network connection or have a network connection running constantly, some programs need to connect to the system via the localhost loopback interface.

Figure 17.15. Hosts Configuration

Tip

To change lookup order, edit the /etc/host.conf file. The line order hosts, bind specifies that /etc/hosts takes precedence over the name servers. Changing the line to order bind, hosts configures the system to resolve hostnames and IP addresses using the name servers first. If the IP address cannot be resolved through the name servers, the system then looks for the IP address in the /etc/hosts file.

17.10. Working with Profiles

Multiple logical network devices can be created for each physical hardware device. For example, if you have one Ethernet card in your system (eth0), you can create logical network devices with different nicknames and different configuration options, all to be specifically associated with eth0.

Logical network devices are different from device aliases. Logical network devices associated with the same physical device must exist in different profiles and cannot be activated simultaneously. Device aliases are also associated with the same physical hardware device, but device aliases associated with the same physical hardware can be activated at the same time. Refer to Section 17.11, “Device Aliases” for details about creating device aliases.

Profiles can be used to create multiple configuration sets for different networks. A configuration set can include logical devices as well as hosts and DNS settings. After configuring the profiles, you can use the Network Administration Tool to switch back and forth between them.

By default, there is one profile called Common. To create a new profile, select Profile => New from the pull-down menu, and enter a unique name for the profile.

You are now modifying the new profile as indicated by the status bar at the bottom of the main window.

Click on an existing device already in the list and click the Copy button to copy the existing device to a logical network device. If you use the New button, a network alias is created, which is incorrect. To change the properties of the logical device, select it from the list and click Edit. For example, the nickname can be changed to a more descriptive name, such as eth0_office, so that it can be recognized more easily.

In the list of devices, there is a column of checkboxes labeled Profile. For each profile, you can check or uncheck devices. Only the checked devices are included for the currently selected profile. For example, if you create a logical device named eth0_office in a profile called Office and want to activate the logical device if the profile is selected, uncheck the eth0 device and check the eth0_office device.

For example, Figure 17.16, “Office Profile” shows a profile called Office with the logical device eth0_office. It is configured to activate the first Ethernet card using DHCP.

Figure 17.16. Office Profile

Notice that the Home profile as shown in Figure 17.17, “Home Profile” activates the eth0_home logical device, which is associated with eth0.

Figure 17.17. Home Profile

You can also configure eth0 to activate in the Office profile only and to activate a PPP (modem) device in the Home profile only. Another example is to have the Common profile activate eth0 and an Away profile activate a PPP device for use while traveling.

To activate a profile at boot time, modify the boot loader configuration file to include the netprofile=<profilename> option. For example, if the system uses GRUB as the boot loader and /boot/grub/grub.conf contains:

To switch profiles after the system has booted, go to Applications (the main menu on the
panel) => System Tools => Network Device Control (or type the command system-control-network) to select a profile and activate it. The activate profile section only appears in the Network Device Control interface if more than the default Common interface exists.

Alternatively, execute the following command to enable a profile (replace <profilename> with the name of the profile):

system-config-network-cmd --profile <profilename> --activate

17.11. Device Aliases

Device aliases are virtual devices associated with the same physical hardware, but they can be activated at the same time to have different IP addresses. They are commonly represented as the device name followed by a colon and a number (for example, eth0:1). They are useful if you want to have multiple IP addresses for a system that only has one network card.

After configuring the Ethernet device —such as eth0 —to use a static IP address (DHCP does not work with aliases), go to the Devices tab and click New. Select the Ethernet card to configure with an alias, set the static IP address for the alias, and click Apply to create it. Since a device already exists for the Ethernet card, the one just created is the alias, such as eth0:1.

Warning

If you are configuring an Ethernet device to have an alias, neither the device nor the alias can be configured to use DHCP. You must configure the IP addresses manually.

Figure 17.18, “Network Device Alias Example” shows an example of one alias for the eth0 device. Notice the eth0:1 device — the first alias for eth0. The second alias for eth0 would have the device name eth0:2, and so on. To modify the settings for the device alias, such as whether to activate it at boot time and the alias number, select it from the list and click the Edit button.

Figure 17.18. Network Device Alias Example

Select the alias and click the Activate button to activate the alias. If you have configured multiple profiles, select which profiles in which to include it.

To verify that the alias has been activated, use the command /sbin/ifconfig. The output should show the device and the device alias with different IP addresses:

17.12. Saving and Restoring the Network Configuration

The command line version of Network Administration Tool can be used to save the system's network configuration to a file. This file can then be used to restore the network settings to a Red Hat Enterprise Linux system.

This feature can be used as part of an automated backup script, to save the configuration before upgrading or reinstalling, or to copy the configuration to a different Red Hat Enterprise Linux system.

To save, or export, the network configuration of a system to the file /tmp/network-config, execute the following command as root:

system-config-network-cmd -e > /tmp/network-config

To restore, or import, the network configuration from the file created from the previous command, execute the following command as root:

system-config-network-cmd -i -c -f /tmp/network-config

The -i option means to import the data, the -c option means to clear the existing configuration prior to importing, and the -f option specifies that the file to import is as follows.

Information security is commonly thought of as a process and not a product. However, standard security implementations usually employ some form of dedicated mechanism to control access privileges and restrict network resources to users who are authorized, identifiable, and traceable. Red Hat Enterprise Linux includes several tools to assist administrators and security engineers with network-level access control issues.

Firewalls are one of the core components of a network security implementation. Several vendors market firewall solutions catering to all levels of the marketplace: from home users protecting one PC to data center solutions safeguarding vital enterprise information. Firewalls can be stand-alone hardware solutions, such as firewall appliances by Cisco, Nokia, and Sonicwall. Vendors such as Checkpoint, McAfee, and Symantec have also developed proprietary software firewall solutions for home and business markets.

Apart from the differences between hardware and software firewalls, there are also differences in the way firewalls function that separate one solution from another. Table 18.1, “Firewall Types” details three common types of firewalls and how they function:

Table 18.1. Firewall Types

Method

Description

Advantages

Disadvantages

NAT

Network Address Translation (NAT) places private IP subnetworks behind one or a small pool of public IP addresses, masquerading all requests to one source rather than several. The Linux kernel has built-in NAT functionality through the Netfilter kernel subsystem.

· Can be configured transparently to machines on a LAN

· Protection of many machines and services behind one or more external IP addresses simplifies administration duties

· Restriction of user access to and from the LAN can be configured by opening and closing ports on the NAT firewall/gateway

· Cannot prevent malicious activity once users connect to a service outside of the firewall

Packet Filter

A packet filtering firewall reads each data packet that passes through a LAN. It can read and process packets by header information and filters the packet based on sets of programmable rules implemented by the firewall administrator. The Linux kernel has built-in packet filtering functionality through the Netfilter kernel subsystem.

· Customizable through the iptables front-end utility

· Does not require any customization on the client side, as all network activity is filtered at the router level rather than the application level

· Since packets are not transmitted through a proxy, network performance is faster due to direct connection from client to remote host

· Cannot filter packets for content like proxy firewalls

· Processes packets at the protocol layer, but cannot filter packets at an application layer

· Complex network architectures can make establishing packet filtering rules difficult, especially if coupled with IP masquerading or local subnets and DMZ networks

Proxy

Proxy firewalls filter all requests of a certain protocol or type from LAN clients to a proxy machine, which then makes those requests to the Internet on behalf of the local client. A proxy machine acts as a buffer between malicious remote users and the internal network client machines.

· Gives administrators control over what applications and protocols function outside of the LAN

· Some proxy servers can cache frequently-accessed data locally rather than having to use the Internet connection to request it. This helps to reduce bandwidth consumption

· Proxy services can be logged and monitored closely, allowing tighter control over resource utilization on the network

· Application services cannot run behind a proxy, so your application servers must use a separate form of network security

· Proxies can become a network bottleneck, as all requests and transmissions are passed through one source rather than directly from a client to a remote service

18.1. Netfilter and IPTables

The Linux kernel features a powerful networking subsystem called Netfilter. The Netfilter subsystem provides stateful or stateless packet filtering as well as NAT and IP masquerading services. Netfilter also has the ability to mangle IP header information for advanced routing and connection state management. Netfilter is controlled using the iptables tool.

18.1.1. IPTables Overview

The power and flexibility of Netfilter is implemented using the iptables administration tool, a command line tool similar in syntax to its predecessor, ipchains.

By contrast, iptables uses the Netfilter subsystem to enhance network connection, inspection, and processing. iptables features advanced logging, pre- and post-routing actions, network address translation, and port forwarding, all in one command line interface.

This section provides an overview of iptables.

18.2. Basic Firewall Configuration

Just as a firewall in a building attempts to prevent a fire from spreading, a computer firewall attempts to prevent malicious software from spreading to your computer. It also helps to prevent unauthorized users from accessing your computer.

In a default Red Hat Enterprise Linux installation, a firewall exists between your computer or network and any untrusted networks, for example the Internet. It determines which services on your computer remote users can access. A properly configured firewall can greatly increase the security of your system. It is recommended that you configure a firewall for any Red Hat Enterprise Linux system with an Internet connection.

18.2.1. Security Level Configuration Tool

During the Firewall Configuration screen of the Red Hat Enterprise Linux installation, you were given the option to enable a basic firewall as well as to allow specific devices, incoming services, and ports.

After installation, you can change this preference by using the Security Level Configuration Tool.

To start this application, use the following command:

[root@myServer ~] # system-config-selinux

Figure 18.1. Security Level Configuration Tool

Note

The Security Level Configuration Tool only configures a basic firewall.

18.2.2. Enabling and Disabling the Firewall

Select one of the following options for the firewall:

Disabled — Disabling the firewall provides complete access to your system and does no security checking. This should only be selected if you are running on a trusted network (not the Internet) or need to configure a custom firewall using the iptables command line tool.

Warning

Firewall configurations and any customized firewall rules are stored in the /etc/sysconfig/iptables file. If you choose Disabled and click OK, these configurations and firewall rules will be lost.

Enabled — This option configures the system to reject incoming connections that are not in response to outbound requests, such as DNS replies or DHCP requests. If access to services running on this machine is needed, you can choose to allow specific services through the firewall.

If you are connecting your system to the Internet, but do not plan to run a server, this is the safest choice.

18.2.3. Trusted Services

Enabling options in the Trusted services list allows the specified service to pass through the firewall.

WWW (HTTP)

The HTTP protocol is used by Apache (and by other Web servers) to serve web pages. If you plan on making your Web server publicly available, select this check box. This option is not required for viewing pages locally or for developing web pages. This service requires that the httpd package be installed.

Enabling WWW (HTTP) will not open a port for HTTPS, the SSL version of HTTP. If this service is required, select the Secure WWW (HTTPS) check box.

FTP

The FTP protocol is used to transfer files between machines on a network. If you plan on making your FTP server publicly available, select this check box. This service requires that the vsftpd package be installed.

SSH

Secure Shell (SSH) is a suite of tools for logging into and executing commands on a remote machine. To allow remote access to the machine via ssh, select this check box. This service requires that the openssh-server package be installed.

Telnet

Telnet is a protocol for logging into remote machines. Telnet communications are unencrypted and provide no security from network snooping. Allowing incoming Telnet access is not recommended. To allow remote access to the machine via telnet, select this check box. This service requires that the telnet-server package be installed.

Mail (SMTP)

SMTP is a protocol that allows remote hosts to connect directly to your machine to deliver mail. You do not need to enable this service if you collect your mail from your ISP's server using POP3 or IMAP, or if you use a tool such as fetchmail. To allow delivery of mail to your machine, select this check box. Note that an improperly configured SMTP server can allow remote machines to use your server to send spam.

NFS4

The Network File System (NFS) is a file sharing protocol commonly used on *NIX systems. Version 4 of this protocol is more secure than its predecessors. If you want to share files or directories on your system with other network users, select this check box.

Samba

Samba is an implementation of Microsoft's proprietary SMB networking protocol. If you need to share files, directories, or locally-connected printers with Microsoft Windows machines, select this check box.

18.2.4. Other Ports

The Security Level Configuration Tool includes an Other ports section for specifying custom IP ports as being trusted by iptables. For example, to allow IRC and Internet printing protocol (IPP) to pass through the firewall, add the following to the Other ports section:

194:tcp,631:tcp

18.2.5. Saving the Settings

Click OK to save the changes and enable or disable the firewall. If Enable firewall was selected, the options selected are translated to iptables commands and written to the /etc/sysconfig/iptables file. The iptables service is also started so that the firewall is activated immediately after saving the selected options. If Disable firewall was selected, the /etc/sysconfig/iptables file is removed and the iptables service is stopped immediately.

The selected options are also written to the /etc/sysconfig/system-config-selinux file so that the settings can be restored the next time the application is started. Do not edit this file by hand.

18.2.6. Activating the IPTables Service

The firewall rules are only active if the iptables service is running. To manually start the service, use the following command:

[root@myServer ~] # service iptables restart

To ensure that iptables starts when the system is booted, use the following command:

[root@myServer ~] # chkconfig --level 345 iptables on

The ipchains service is not included in Red Hat Enterprise Linux. However, if ipchains is installed (for example, an upgrade was performed and the system had ipchains previously installed), the ipchains and iptables services should not be activated simultaneously. To make sure the ipchains service is disabled and configured not to start at boot time, use the following two commands:

18.3. Using IPTables

The first step in using iptables is to start the iptables service. Use the following command to start the iptables service:

[root@myServer ~] # service iptables start

Note

The ip6tables service can be turned off if you intend to use the iptables service only. If you deactivate the ip6tables service, remember to deactivate the IPv6 network also. Never leave a network device active without the matching firewall.

To force iptables to start by default when the system is booted, use the following command:

[root@myServer ~] # chkconfig --level 345 iptables on

This forces iptables to start whenever the system is booted into runlevel 3, 4, or 5.

18.3.1. IPTables Command Syntax

The following sample iptables command illustrates the basic command syntax:

[root@myServer ~ ] # iptables -A <chain> -j <target>

The -A option specifies that the rule be appended to <chain>. Each chain is comprised of one or more rules, and is therefore also known as a ruleset.

The three built-in chains are INPUT, OUTPUT, and FORWARD. These chains are permanent and cannot be deleted. The chain specifies the point at which a packet is manipulated.

The -j <target> option specifies the target of the rule; i.e., what to do if the packet matches the rule. Examples of built-in targets are ACCEPT, DROP, and REJECT.

Refer to the iptables man page for more information on the available chains, options, and targets.

18.3.2. Basic Firewall Policies

Establishing basic firewall policies creates a foundation for building more detailed, user-defined rules.

Each iptables chain is comprised of a default policy, and zero or more rules which work in concert with the default policy to define the overall ruleset for the firewall.

The default policy for a chain can be either DROP or ACCEPT. Security-minded administrators typically implement a default policy of DROP, and only allow specific packets on a case-by-case basis. For example, the following policies block all incoming and outgoing packets on a network gateway:

It is also recommended that any forwarded packets — network traffic that is to be routed from the firewall to its destination node — be denied as well, to restrict internal clients from inadvertent exposure to the Internet. To do this, use the following rule:

[root@myServer ~ ] # iptables -P FORWARD DROP

When you have established the default policies for each chain, you can create and save further rules for your particular network and security requirements.

The following sections describe how to save iptables rules and outline some of the rules you might implement in the course of building your iptables firewall.

18.3.3. Saving and Restoring IPTables Rules

Changes to iptables are transitory; if the system is rebooted or if the iptables service is restarted, the rules are automatically flushed and reset. To save the rules so that they are loaded when the iptables service is started, use the following command:

[root@myServer ~ ] # service iptables save

The rules are stored in the file /etc/sysconfig/iptables and are applied whenever the service is started or the machine is rebooted.

18.4. Common IPTables Filtering

Preventing remote attackers from accessing a LAN is one of the most important aspects of network security. The integrity of a LAN should be protected from malicious remote users through the use of stringent firewall rules.

However, with a default policy set to block all incoming, outgoing, and forwarded packets, it is impossible for the firewall/gateway and internal LAN users to communicate with each other or with external resources.

To allow users to perform network-related functions and to use networking applications, administrators must open certain ports for communication.

For example, to allow access to port 80 on the firewall, append the following rule:

This allows users to browse websites that communicate using the standard port 80. To allow access to secure websites (for example, https://www.example.com/), you also need to provide access to port 443, as follows:

If a rule specifies that any packets from the 192.168.100.0/24 subnet be dropped, and this is followed by a rule that allows packets from 192.168.100.13 (which is within the dropped subnet), then the second rule is ignored.

The rule to allow packets from 192.168.100.13 must precede the rule that drops the remainder of the subnet.

To insert a rule in a specific location in an existing chain, use the -I option. For example:

[root@myServer ~ ] # iptables -I INPUT 1 -i lo -p all -j ACCEPT

This rule is inserted as the first rule in the INPUT chain to allow local loopback device traffic.

There may be times when you require remote access to the LAN. Secure services, for example SSH, can be used for encrypted remote connection to LAN services.

Administrators with PPP-based resources (such as modem banks or bulk ISP accounts), dial-up access can be used to securely circumvent firewall barriers. Because they are direct connections, modem connections are typically behind a firewall/gateway.

For remote users with broadband connections, however, special cases can be made. You can configure iptables to accept connections from remote SSH clients. For example, the following rules allow remote SSH access:

These rules allow incoming and outbound access for an individual system, such as a single PC directly connected to the Internet or a firewall/gateway. However, they do not allow nodes behind the firewall/gateway to access these services. To allow LAN access to these services, you can use Network Address Translation (NAT) with iptables filtering rules.

18.5. FORWARD and NAT Rules

Most ISPs provide only a limited number of publicly routable IP addresses to the organizations they serve.

Administrators must, therefore, find alternative ways to share access to Internet services without giving public IP addresses to every node on the LAN. Using private IP addresses is the most common way of allowing all nodes on a LAN to properly access internal and external network services.

Edge routers (such as firewalls) can receive incoming transmissions from the Internet and route the packets to the intended LAN node. At the same time, firewalls/gateways can also route outgoing requests from a LAN node to the remote Internet service.

This forwarding of network traffic can become dangerous at times, especially with the availability of modern cracking tools that can spoof internal IP addresses and make the remote attacker's machine act as a node on your LAN.

To prevent this, iptables provides routing and forwarding policies that can be implemented to prevent abnormal usage of network resources.

The FORWARD chain allows an administrator to control where packets can be routed within a LAN. For example, to allow forwarding for the entire LAN (assuming the firewall/gateway is assigned an internal IP address on eth1), use the following rules:

This rule gives systems behind the firewall/gateway access to the internal network. The gateway routes packets from one LAN node to its intended destination node, passing all packets through its eth1 device.

Note

By default, the IPv4 policy in Red Hat Enterprise Linux kernels disables support for IP forwarding. This prevents machines that run Red Hat Enterprise Linux from functioning as dedicated edge routers. To enable IP forwarding, use the following command:

[root@myServer ~ ] # sysctl -w net.ipv4.ip_forward=1

This configuration change is only valid for the current session; it does not persist beyond a reboot or network service restart. To permanently set IP forwarding, edit the /etc/sysctl.conf file as follows:

Locate the following line:

net.ipv4.ip_forward = 0

Edit it to read as follows:

net.ipv4.ip_forward = 1

Use the following command to enable the change to the sysctl.conf file:

[root@myServer ~ ] # sysctl -p /etc/sysctl.conf

18.5.1. Postrouting and IP Masquerading

Accepting forwarded packets via the firewall's internal IP device allows LAN nodes to communicate with each other; however they still cannot communicate externally to the Internet.

To allow LAN nodes with private IP addresses to communicate with external public networks, configure the firewall for IP masquerading, which masks requests from LAN nodes with the IP address of the firewall's external device (in this case, eth0):

POSTROUTING allows packets to be altered as they are leaving the firewall's external device.

The -j MASQUERADE target is specified to mask the private IP address of a node with the external IP address of the firewall/gateway.

18.5.2. Prerouting

If you have a server on your internal network that you want make available externally, you can use the -j DNAT target of the PREROUTING chain in NAT to specify a destination IP address and port where incoming packets requesting a connection to your internal service can be forwarded.

For example, if you want to forward incoming HTTP requests to your dedicated Apache HTTP Server at 172.31.0.23, use the following command:

This rule specifies that the nat table use the built-in PREROUTING chain to forward incoming HTTP requests exclusively to the listed destination IP address of 172.31.0.23.

Note

If you have a default policy of DROP in your FORWARD chain, you must append a rule to forward all incoming HTTP requests so that destination NAT routing is possible. To do this, use the following command:

This rule forwards all incoming HTTP requests from the firewall to the intended destination; the Apache HTTP Server behind the firewall.

18.5.3. DMZs and IPTables

You can create iptables rules to route traffic to certain machines, such as a dedicated HTTP or FTP server, in a demilitarized zone (DMZ). A DMZ is a special local subnetwork dedicated to providing services on a public carrier, such as the Internet.

For example, to set a rule for routing incoming HTTP requests to a dedicated HTTP server at 10.0.4.2 (outside of the 192.168.1.0/24 range of the LAN), NAT uses the PREROUTING table to forward the packets to the appropriate destination:

With this command, all HTTP connections to port 80 from outside of the LAN are routed to the HTTP server on a network separate from the rest of the internal network. This form of network segmentation can prove safer than allowing HTTP connections to a machine on the network.

If the HTTP server is configured to accept secure connections, then port 443 must be forwarded as well.

18.6. Malicious Software and Spoofed IP Addresses

More elaborate rules can be created that control access to specific subnets, or even specific nodes, within a LAN. You can also restrict certain dubious applications or programs such as trojans, worms, and other client/server viruses from contacting their server.

For example, some trojans scan networks for services on ports from 31337 to 31340 (called the elite ports in cracking terminology).

Since there are no legitimate services that communicate via these non-standard ports, blocking them can effectively diminish the chances that potentially infected nodes on your network independently communicate with their remote master servers.

The following rules drop all TCP traffic that attempts to use port 31337:

You can also block outside connections that attempt to spoof private IP address ranges to infiltrate your LAN.

For example, if your LAN uses the 192.168.1.0/24 range, you can design a rule that instructs the Internet-facing network device (for example, eth0) to drop any packets to that device with an address in your LAN IP range.

Because it is recommended to reject forwarded packets as a default policy, any other spoofed IP address to the external-facing device (eth0) is rejected automatically.

There is a distinction between the DROP and REJECT targets when dealing with appended rules.

The REJECT target denies access and returns a connection refused error to users who attempt to connect to the service. The DROP target, as the name implies, drops the packet without any warning.

Administrators can use their own discretion when using these targets. However, to avoid user confusion and attempts to continue connecting, the REJECT target is recommended.

18.7. IPTables and Connection Tracking

You can inspect and restrict connections to services based on their connection state. A module within iptables uses a method called connection tracking to store information about incoming connections. You can allow or deny access based on the following connection states:

NEW — A packet requesting a new connection, such as an HTTP request.

ESTABLISHED — A packet that is part of an existing connection.

RELATED — A packet that is requesting a new connection but is part of an existing connection. For example, FTP uses port 21 to establish a connection, but data is transferred on a different port (typically port 20).

INVALID — A packet that is not part of any connections in the connection tracking table.

You can use the stateful functionality of iptables connection tracking with any network protocol, even if the protocol itself is stateless (such as UDP). The following example shows a rule that uses connection tracking to forward only the packets that are associated with an established connection:

18.8. IPv6

The introduction of the next-generation Internet Protocol, called IPv6, expands beyond the 32-bit address limit of IPv4 (or IP). IPv6 supports 128-bit addresses, and carrier networks that are IPv6 aware are therefore able to address a larger number of routable addresses than IPv4.

The ip6tables command syntax is identical to iptables in every aspect except that it supports 128-bit addresses. For example, use the following command to enable SSH connections on an IPv6-aware network server:

18.9.3. Related Documentation

Red Hat Linux Firewalls, by Bill McCarty; Red Hat Press — a comprehensive reference to building network and server firewalls using open source packet filtering technology such as Netfilter and iptables. It includes topics that cover analyzing firewall logs, developing firewall rules, and customizing your firewall using various graphical tools.

Linux Firewalls, by Robert Ziegler; New Riders Press — contains a wealth of information on building firewalls using both 2.2 kernel ipchains as well as Netfilter and iptables. Additional security topics such as remote access issues and intrusion detection systems are also covered.

Maintaining security on your system is extremely important, and one approach for this task is to manage access to system services carefully. Your system may need to provide open access to particular services (for example, httpd if you are running a Web server). However, if you do not need to provide a service, you should turn it off to minimize your exposure to possible bug exploits.

There are several different methods for managing access to system services. Decide which method of management to use based on the service, your system's configuration, and your level of Linux expertise.

The easiest way to deny access to a service is to turn it off. Both the services managed by xinetd and the services in the /etc/rc.d/init.d hierarchy (also known as SysV services) can be configured to start or stop using three different applications:

Services Configuration Tool — a graphical application that displays a description of each service, displays whether each service is started at boot time (for runlevels 3, 4, and 5), and allows services to be started, stopped, and restarted.

ntsysv — a text-based application that allows you to configure which services are started at boot time for each runlevel. Non-xinetd services can not be started, stopped, or restarted using this program.

chkconfig — a command line utility that allows you to turn services on and off for the different runlevels. Non-xinetd services can not be started, stopped, or restarted using this utility.

You may find that these tools are easier to use than the alternatives — editing the numerous symbolic links located in the directories below /etc/rc.d by hand or editing the xinetd configuration files in /etc/xinetd.d.

Another way to manage access to system services is by using iptables to configure an IP firewall. If you are a new Linux user, please realize that iptables may not be the best solution for you. Setting up iptables can be complicated and is best tackled by experienced Linux system administrators.

On the other hand, the benefit of using iptables is flexibility. For example, if you need a customized solution which provides certain hosts access to certain services, iptables can provide it for you. Refer to the Reference Guide and the Security Guide for more information about iptables.

Alternatively, if you are looking for a utility to set general access rules for your home machine, and/or if you are new to Linux, try the Security Level Configuration Tool (system-config-securitylevel), which allows you to select the security level for your system, similar to the Firewall Configuration screen in the installation program.

If you need more specific firewall rules, refer to the iptables chapter in the Reference Guide.

19.1. Runlevels

Before you can configure access to services, you must understand Linux runlevels. A runlevel is a state, or mode, that is defined by the services listed in the directory /etc/rc.d/rc<x>.d, where <x> is the number of the runlevel.

The following runlevels exist:

0 — Halt

1 — Single-user mode

2 — Not used (user-definable)

3 — Full multi-user mode

4 — Not used (user-definable)

5 — Full multi-user mode (with an X-based login screen)

6 — Reboot

If you use a text login screen, you are operating in runlevel 3. If you use a graphical login screen, you are operating in runlevel 5.

The default runlevel can be changed by modifying the /etc/inittab file, which contains a line near the top of the file similar to the following:

id:5:initdefault:

Change the number in this line to the desired runlevel. The change does not take effect until you reboot the system.

To change the runlevel immediately, use the command telinit followed by the runlevel number. You must be root to use this command. The telinit command does not change the /etc/inittab file; it only changes the runlevel currently running. When the system is rebooted, it continues to boot the runlevel as specified in /etc/inittab.

19.2. TCP Wrappers

Many UNIX system administrators are accustomed to using TCP wrappers to manage access to certain network services. Any network services managed by xinetd (as well as any program with built-in support for libwrap) can use TCP wrappers to manage access. xinetd can use the /etc/hosts.allow and /etc/hosts.deny files to configure access to system services. As the names imply, hosts.allow contains a list of rules that allow clients to access the network services controlled by xinetd, and hosts.deny contains rules to deny access. The hosts.allow file takes precedence over the hosts.deny file. Permissions to grant or deny access can be based on individual IP address (or hostnames) or on a pattern of clients. Refer to the Reference Guide and hosts_access in section 5 of the man pages (man 5 hosts_access) for details.

19.2.1. xinetd

To control access to Internet services, use xinetd, which is a secure replacement for inetd. The xinetd daemon conserves system resources, provides access control and logging, and can be used to start special-purpose servers. xinetd can be used to provide access only to particular hosts, to deny access to particular hosts, to provide access to a service at certain times, to limit the rate of incoming connections and/or the load created by connections, and more

xinetd runs constantly and listens on all ports for the services it manages. When a connection request arrives for one of its managed services, xinetd starts up the appropriate server for that service.

The configuration file for xinetd is /etc/xinetd.conf, but the file only contains a few defaults and an instruction to include the /etc/xinetd.d directory. To enable or disable an xinetd service, edit its configuration file in the /etc/xinetd.d directory. If the disable attribute is set to yes, the service is disabled. If the disable attribute is set to no, the service is enabled. You can edit any of the xinetd configuration files or change its enabled status using the Services Configuration Tool, ntsysv, or chkconfig. For a list of network services controlled by xinetd, review the contents of the /etc/xinetd.d directory with the command ls /etc/xinetd.d.

19.3. Services Configuration Tool

The Services Configuration Tool is a graphical application developed by Red Hat, Inc to configure which SysV services in the /etc/rc.d/init.d directory are started at boot time (for runlevels 3, 4, and 5) and which xinetd services are enabled. It also allows you to start, stop, and restart SysV services as well as restart xinetd.

To start the Services Configuration Tool from the desktop, go to the Main Menu Button (on the Panel) => System Settings => Server Settings => Services or type the command system-config-services at a shell prompt (for example, in an XTerm or a GNOME terminal).

Figure 19.1. Services Configuration Tool

The Services Configuration Tool displays the current runlevel as well as the runlevel you are currently editing. To edit a different runlevel, select Edit Runlevel from the pulldown menu and select runlevel 3, 4, or 5. Refer to Section 19.1, “Runlevels” for a description of runlevels.

The Services Configuration Tool lists the services from the /etc/rc.d/init.d directory as well as the services controlled by xinetd. Click on the name of the service from the list on the left-hand side of the application to display a brief description of that service as well as the status of the service. If the service is not an xinetd service, the status window shows whether the service is currently running. If the service is controlled by xinetd, the status window displays the phrase xinetd service.

To start, stop, or restart a service immediately, select the service from the list and click the appropriate button on the toolbar (or choose the action from the Actions pulldown menu). If the service is an xinetd service, the action buttons are disabled because they can not be started or stopped individually.

If you enable/disable an xinetd service by checking or unchecking the checkbox next to the service name, you must select File => Save Changes from the pulldown menu to restart xinetd and immediately enable/disable the xinetd service that you changed. xinetd is also configured to remember the setting. You can enable/disable multiple xinetd services at a time and save the changes when you are finished.

For example, assume you check rsync to enable it in runlevel 3 and then save the changes. The rsync service is immediately enabled. The next time xinetd is started, rsync is still enabled.

Warning

When you save changes to xinetd services, xinetd is restarted, and the changes take place immediately. When you save changes to other services, the runlevel is reconfigured, but the changes do not take effect immediately.

To enable a non-xinetd service to start at boot time for the currently selected runlevel, check the checkbox beside the name of the service in the list. After configuring the runlevel, apply the changes by selecting File => Save Changes from the pulldown menu. The runlevel configuration is changed, but the runlevel is not restarted; thus, the changes do not take place immediately.

For example, assume you are configuring runlevel 3. If you change the value for the httpd service from checked to unchecked and then select Save Changes, the runlevel 3 configuration changes so that httpd is not started at boot time. However, runlevel 3 is not reinitialized, so httpd is still running. Select one of following options at this point:

Stop the httpd service — Stop the service by selecting it from the list and clicking the Stop button. A message appears stating that the service was stopped successfully.

Reinitialize the runlevel — Reinitialize the runlevel by going to a shell prompt and typing the command telinit 3 (where 3 is the runlevel number). This option is recommended if you change the Start at Boot value of multiple services and want to activate the changes immediately.

Do nothing else — You do not have to stop the httpd service. You can wait until the system is rebooted for the service to stop. The next time the system is booted, the runlevel is initialized without the httpd service running.

To add a service to a runlevel, select the runlevel from the Edit Runlevel pulldown menu, and then select Actions => Add Service. To delete a service from a runlevel, select the runlevel from the Edit Runlevel pulldown menu, select the service to be deleted from the list on the left, and select Actions => Delete Service.

19.4. ntsysv

The ntsysv utility provides a simple interface for activating or deactivating services. You can use ntsysv to turn an xinetd-managed service on or off. You can also use ntsysv to configure runlevels. By default, only the current runlevel is configured. To configure a different runlevel, specify one or more runlevels with the --level option. For example, the command ntsysv --level 345 configures runlevels 3, 4, and 5.

The ntsysv interface works like the text mode installation program. Use the up and down arrows to navigate up and down the list. The space bar selects/unselects services and is also used to "press" the Ok and Cancel buttons. To move between the list of services and the Ok and Cancel buttons, use the Tab key. A * signifies that a service is set to on. Pressing the F1 key displays a short description of the selected service.

Warning

Services managed by xinetd are immediately affected by ntsysv. For all other services, changes do not take effect immediately. You must stop or start the individual service with the command service daemon stop. In the previous example, replace daemon with the name of the service you want to stop; for example, httpd. Replace stop with start or restart to start or restart the service.

19.5. chkconfig

The chkconfig command can also be used to activate and deactivate services. The chkconfig --list command displays a list of system services and whether they are started (on) or stopped (off) in runlevels 0-6. At the end of the list is a section for the services managed by xinetd.

If the chkconfig --list command is used to query a service managed by xinetd, it displays whether the xinetd service is enabled (on) or disabled (off). For example, the command chkconfig --list finger returns the following output:

finger on

As shown, finger is enabled as an xinetd service. If xinetd is running, finger is enabled.

If you use chkconfig --list to query a service in /etc/rc.d, service's settings for each runlevel are displayed. For example, the command chkconfig --list httpd returns the following output:

httpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off

chkconfig can also be used to configure a service to be started (or not) in a specific runlevel. For example, to turn nscd off in runlevels 3, 4, and 5, use the following command:

chkconfig --level 345 nscd off

Warning

Services managed by xinetd are immediately affected by chkconfig. For example, if xinetd is running, finger is disabled, and the command chkconfig finger on is executed, finger is immediately enabled without having to restart xinetd manually. Changes for other services do not take effect immediately after using chkconfig. You must stop or start the individual service with the command service daemon stop. In the previous example, replace daemon with the name of the service you want to stop; for example, httpd. Replace stop with start or restart to start or restart the service.

19.6. Additional Resources

For more information, refer to the following resources.

19.6.1. Installed Documentation

The man pages for ntsysv, chkconfig, xinetd, and xinetd.conf.

man 5 hosts_access — The man page for the format of host access control files (in section 5 of the man pages).

19.6.2. Useful Websites

http://www.xinetd.org — The xinetd webpage. It contains a more detailed list of features and sample configuration files.

19.6.3. Related Books

Reference Guide , Red Hat, Inc — This companion manual contains detailed information about how TCP wrappers and xinetd allow or deny access as well as how to configure network access using them. It also provides instructions for creating iptables firewall rules.

OpenSSH is a free, open source implementation of the SSH (S ecure SH ell) protocols. It replaces telnet, ftp, rlogin, rsh, and rcp with secure, encrypted network connectivity tools. OpenSSH supports versions 1.3, 1.5, and 2 of the SSH protocol. Since OpenSSH version 2.9, the default protocol is version 2, which uses RSA keys as the default.

20.1. Why Use OpenSSH?

If you use OpenSSH tools, you are enhancing the security of your machine. All communications using OpenSSH tools, including passwords, are encrypted. Telnet and ftp use plain text passwords and send all information unencrypted. The information can be intercepted, the passwords can be retrieved, and your system could be compromised by an unauthorized person logging in to your system using one of the intercepted passwords. The OpenSSH set of utilities should be used whenever possible to avoid these security problems.

Another reason to use OpenSSH is that it automatically forwards the DISPLAY variable to the client machine. In other words, if you are running the X Window System on your local machine, and you log in to a remote machine using the ssh command, when you run a program on the remote machine that requires X, it will be displayed on your local machine. This feature is convenient if you prefer graphical system administration tools but do not always have physical access to your server.

20.2. Configuring an OpenSSH Server

To run an OpenSSH server, you must first make sure that you have the proper RPM packages installed. The openssh-server package is required and depends on the openssh package.

The OpenSSH daemon uses the configuration file /etc/ssh/sshd_config. The default configuration file should be sufficient for most purposes. If you want to configure the daemon in ways not provided by the default sshd_config, read the sshd man page for a list of the keywords that can be defined in the configuration file.

To start the OpenSSH service, use the command /sbin/service sshd start. To stop the OpenSSH server, use the command /sbin/service sshd stop. If you want the daemon to start automatically at boot time, refer to Chapter 19, Controlling Access to Services for information on how to manage services.

If you reinstall, the reinstalled system creates a new set of identification keys. Any clients who had connected to the system with any of the OpenSSH tools before the reinstall will see the following message:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.

If you want to keep the host keys generated for the system, backup the /etc/ssh/ssh_host*key* files and restore them after the reinstall. This process retains the system's identity, and when clients try to connect to the system after the reinstall, they will not receive the warning message.

20.3. Configuring an OpenSSH Client

To connect to an OpenSSH server from a client machine, you must have the openssh-clients and openssh packages installed on the client machine.

20.3.1. Using the ssh Command

The ssh command is a secure replacement for the rlogin, rsh, and telnet commands. It allows you to log in to a remote machine as well as execute commands on a remote machine.

Logging in to a remote machine with ssh is similar to using telnet. To log in to a remote machine named penguin.example.net, type the following command at a shell prompt:

ssh penguin.example.net

The first time you ssh to a remote machine, you will see a message similar to the following:

The authenticity of host 'penguin.example.net' can't be established.
DSA key fingerprint is 94:68:3a:3a:bc:f3:9a:9b:01:5d:b3:07:38:e2:11:0c.
Are you sure you want to continue connecting (yes/no)?

Type yes to continue. This will add the server to your list of known hosts (~/.ssh/known_hosts/) as seen in the following message:

Warning: Permanently added 'penguin.example.net' (RSA) to the list of known hosts.

Next, you will see a prompt asking for your password for the remote machine. After entering your password, you will be at a shell prompt for the remote machine. If you do not specify a username the username that you are logged in as on the local client machine is passed to the remote machine. If you want to specify a different username, use the following command:

ssh username@penguin.example.net

You can also use the syntax ssh -l username penguin.example.net.

The ssh command can be used to execute a command on the remote machine without logging in to a shell prompt. The syntax is ssh hostnamecommand. For example, if you want to execute the command ls /usr/share/doc on the remote machine penguin.example.net, type the following command at a shell prompt:

ssh penguin.example.net ls /usr/share/doc

After you enter the correct password, the contents of the remote directory /usr/share/doc will be displayed, and you will return to your local shell prompt.

20.3.2. Using the scp Command

The scp command can be used to transfer files between machines over a secure, encrypted connection. It is similar to rcp.

The general syntax to transfer a local file to a remote system is as follows:

scp <localfile>username@tohostname:<remotefile>

The <localfile> specifies the source including path to the file, such as /var/log/maillog. The <remotefile> specifies the destination, which can be a new filename such as /tmp/hostname-maillog. For the remote system, if you do not have a preceding /, the path will be relative to the home directory of username, typically /home/username/.

To transfer the local file shadowman to the home directory of your account on penguin.example.net, type the following at a shell prompt (replace username with your username):

scp shadowman username@penguin.example.net:shadowman

This will transfer the local file shadowman to /home/username/shadowman on penguin.example.net. Alternately, you can leave off the final shadowman in the scp command.

The general syntax to transfer a remote file to the local system is as follows:

scp username@tohostname:<remotefile><newlocalfile>

The <remotefile> specifies the source including path, and <newlocalfile> specifies the destination including path.

Multiple files can be specified as the source files. For example, to transfer the contents of the directory downloads/ to an existing directory called uploads/ on the remote machine penguin.example.net, type the following at a shell prompt:

scp downloads/* username@penguin.example.net:uploads/

20.3.3. Using the sftp Command

The sftp utility can be used to open a secure, interactive FTP session. It is similar to ftp except that it uses a secure, encrypted connection. The general syntax is sftp username@hostname.com. Once authenticated, you can use a set of commands similar to those used by FTP. Refer to the sftp man page for a list of these commands. To read the man page, execute the command man sftp at a shell prompt. The sftp utility is only available in OpenSSH version 2.5.0p1 and higher.

20.3.4. Generating Key Pairs

If you do not want to enter your password every time you use ssh, scp, or sftp to connect to a remote machine, you can generate an authorization key pair.

Keys must be generated for each user. To generate keys for a user, use the following steps as the user who wants to connect to remote machines. If you complete the steps as root, only root will be able to use the keys.

Starting with OpenSSH version 3.0, ~/.ssh/authorized_keys2, ~/.ssh/known_hosts2, and /etc/ssh_known_hosts2 are obsolete. SSH Protocol 1 and 2 share the ~/.ssh/authorized_keys, ~/.ssh/known_hosts, and /etc/ssh/ssh_known_hosts files.

If you reinstall and want to save your generated key pair, backup the .ssh directory in your home directory. After reinstalling, copy this directory back to your home directory. This process can be done for all users on your system, including root.

20.3.4.1. Generating an RSA Key Pair for Version 2

Use the following steps to generate an RSA key pair for version 2 of the SSH protocol. This is the default starting with OpenSSH 2.9.

To generate an RSA key pair to work with version 2 of the protocol, type the following command at a shell prompt:

ssh-keygen -t rsa

Accept the default file location of ~/.ssh/id_rsa. Enter a passphrase different from your account password and confirm it by entering it again.

The public key is written to ~/.ssh/id_rsa.pub. The private key is written to ~/.ssh/id_rsa. Never distribute your private key to anyone.

Change the permissions of the .ssh directory using the following command:

chmod 755 ~/.ssh

Copy the contents of ~/.ssh/id_rsa.pub into the file ~/.ssh/authorized_keys on the machine to which you want to connect. If the file ~/.ssh/authorized_keys exist, append the contents of the file ~/.ssh/id_rsa.pub to the file ~/.ssh/authorized_keys on the other machine.

Change the permissions of the authorized_keys file using the following command:

20.3.4.2. Generating a DSA Key Pair for Version 2

Use the following steps to generate a DSA key pair for version 2 of the SSH Protocol.

To generate a DSA key pair to work with version 2 of the protocol, type the following command at a shell prompt:

ssh-keygen -t dsa

Accept the default file location of ~/.ssh/id_dsa. Enter a passphrase different from your account password and confirm it by entering it again.

Tip

A passphrase is a string of words and characters used to authenticate a user. Passphrases differ from passwords in that you can use spaces or tabs in the passphrase. Passphrases are generally longer than passwords because they are usually phrases instead of a single word.

The public key is written to ~/.ssh/id_dsa.pub. The private key is written to ~/.ssh/id_dsa. It is important never to give anyone the private key.

Change the permissions of the .ssh directory with the following command:

chmod 755 ~/.ssh

Copy the contents of ~/.ssh/id_dsa.pub into the file ~/.ssh/authorized_keys on the machine to which you want to connect. If the file ~/.ssh/authorized_keys exist, append the contents of the file ~/.ssh/id_dsa.pub to the file ~/.ssh/authorized_keys on the other machine.

Change the permissions of the authorized_keys file using the following command:

20.3.4.3. Generating an RSA Key Pair for Version 1.3 and 1.5

Use the following steps to generate an RSA key pair, which is used by version 1 of the SSH Protocol. If you are only connecting between systems that use DSA, you do not need an RSA version 1.3 or RSA version 1.5 key pair.

To generate an RSA (for version 1.3 and 1.5 protocol) key pair, type the following command at a shell prompt:

ssh-keygen -t rsa1

Accept the default file location (~/.ssh/identity). Enter a passphrase different from your account password. Confirm the passphrase by entering it again.

The public key is written to ~/.ssh/identity.pub. The private key is written to ~/.ssh/identity. Do not give anyone the private key.

Change the permissions of your .ssh directory and your key with the commands chmod 755 ~/.ssh and chmod 644 ~/.ssh/identity.pub.

Copy the contents of ~/.ssh/identity.pub into the file ~/.ssh/authorized_keys on the machine to which you wish to connect. If the file ~/.ssh/authorized_keys does not exist, you can copy the file ~/.ssh/identity.pub to the file ~/.ssh/authorized_keys on the remote machine.

20.3.4.4. Configuring ssh-agent with GNOME

The ssh-agent utility can be used to save your passphrase so that you do not have to enter it each time you initiate an ssh or scp connection. If you are using GNOME, the openssh-askpass-gnome package contains the application used to prompt you for your passphrase when you log in to GNOME and save it until you log out of GNOME. You will not have to enter your password or passphrase for any ssh or scp connection made during that GNOME session. If you are not using GNOME, refer to Section 20.3.4.5, “Configuring ssh-agent”.

To save your passphrase during your GNOME session, follow the following steps:

You will need to have the package openssh-askpass-gnome installed; you can use the command rpm -q openssh-askpass-gnome to determine if it is installed or not. If it is not installed, install it from your Red Hat Enterprise Linux CD-ROM set, from a Red Hat FTP mirror site, or using Red Hat Network.

Select Main Menu Button (on the Panel) => Preferences => More Preferences => Sessions, and click on the Startup Programs tab. Click Add and enter /usr/bin/ssh-add in the Startup Command text area. Set it a priority to a number higher than any existing commands to ensure that it is executed last. A good priority number for ssh-add is 70 or higher. The higher the priority number, the lower the priority. If you have other programs listed, this one should have the lowest priority. Click Close to exit the program.

Log out and then log back into GNOME; in other words, restart X. After GNOME is started, a dialog box will appear prompting you for your passphrase(s). Enter the passphrase requested. If you have both DSA and RSA key pairs configured, you will be prompted for both. From this point on, you should not be prompted for a password by ssh, scp, or sftp.

20.3.4.5. Configuring ssh-agent

The ssh-agent can be used to store your passphrase so that you do not have to enter it each time you make a ssh or scp connection. If you are not running the X Window System, follow these steps from a shell prompt. If you are running GNOME but you do not want to configure it to prompt you for your passphrase when you log in (refer to Section 20.3.4.4, “Configuring ssh-agent with GNOME”), this procedure will work in a terminal window, such as an XTerm. If you are running X but not GNOME, this procedure will work in a terminal window. However, your passphrase will only be remembered for that terminal window; it is not a global setting.

At a shell prompt, type the following command:

exec /usr/bin/ssh-agent $SHELL

Then type the command:

ssh-add

and enter your passphrase(s). If you have more than one key pair configured, you will be prompted for each one.

When you log out, your passphrase(s) will be forgotten. You must execute these two commands each time you log in to a virtual console or open a terminal window.

20.4. Additional Resources

The OpenSSH and OpenSSL projects are in constant development, and the most up-to-date information for them is available from their websites. The man pages for OpenSSH and OpenSSL tools are also good sources of detailed information.

20.4.1. Installed Documentation

The ssh, scp, sftp, sshd, and ssh-keygen man pages — These man pages include information on how to use these commands as well as all the parameters that can be used with them.

Network File System (NFS) is a way to share files between machines on a network as if the files were located on the client's local hard drive. Red Hat Enterprise Linux can be both an NFS server and an NFS client, which means that it can export file systems to other systems and mount file systems exported from other machines.

21.1. Why Use NFS?

NFS is useful for sharing directories of files between multiple users on the same network. For example, a group of users working on the same project can have access to the files for that project using a shared directory of the NFS file system (commonly known as an NFS share) mounted in the directory /myproject. To access the shared files, the user goes into the /myproject directory on his machine. There are no passwords to enter or special commands to remember. Users work as if the directory is on their local machines.

21.2. Mounting NFS File Systems

Use the mount command to mount a shared NFS directory from another machine:

mount shadowman.example.com:/misc/export/misc/local

Warning

The mount point directory on the local machine (/misc/local in the above example) must exist before this command can be executed.

In this command, shadowman.example.com is the hostname of the NFS file server, /misc/export is the directory that shadowman is exporting, and /misc/local is the location to mount the file system on the local machine. After the mount command runs (and if the client has proper permissions from the shadowman.example.com NFS server) the client user can execute the command ls /misc/local to display a listing of the files in /misc/export on shadowman.example.com.

21.2.1. Mounting NFS File Systems using /etc/fstab

An alternate way to mount an NFS share from another machine is to add a line to the /etc/fstab file. The line must state the hostname of the NFS server, the directory on the server being exported, and the directory on the local machine where the NFS share is to be mounted. You must be root to modify the /etc/fstab file.

The general syntax for the line in /etc/fstab is as follows:

server:/usr/local/pub /pub nfs rsize=8192,wsize=8192,timeo=14,intr

The mount point /pub must exist on the client machine before this command can be executed. After adding this line to /etc/fstab on the client system, type the command mount /pub at a shell prompt, and the mount point /pub is mounted from the server.

21.2.2. Mounting NFS File Systems using autofs

A third option for mounting an NFS share is the use of the autofs service. Autofs uses the automount daemon to manage your mount points by only mounting them dynamically when they are accessed.

Autofs consults the master map configuration file /etc/auto.master to determine which mount points are defined. It then starts an automount process with the appropriate parameters for each mount point. Each line in the master map defines a mount point and a separate map file that defines the file systems to be mounted under this mount point. For example, the /etc/auto.misc file might define mount points in the /misc directory; this relationship would be defined in the /etc/auto.master file.

Each entry in auto.master has three fields. The first field is the mount point. The second field is the location of the map file, and the third field is optional. The third field can contain information such as a timeout value.

For example, to mount the directory /proj52 on the remote machine penguin.example.net at the mount point /misc/myproject on your machine, add the following line to auto.master:

The first field in /etc/auto.misc is the name of the /misc subdirectory. This subdirectory is created dynamically by automount. It should not actually exist on the client machine. The second field contains mount options such as rw for read and write access. The third field is the location of the NFS export including the hostname and directory.

Note

The directory /misc must exist on the local file system. There should be no subdirectories in /misc on the local file system.

To start the autofs service, at a shell prompt, type the following command:

/sbin/service autofs restart

To view the active mount points, type the following command at a shell prompt:

/sbin/service autofs status

If you modify the /etc/auto.master configuration file while autofs is running, you must tell the automount daemon(s) to reload by typing the following command at a shell prompt:

21.2.3. Using TCP

The default transport protocol for NFSv4 is TCP; however, the Red Hat Enterprise Linux 4 kernel includes support for NFS over UDP. To use NFS over UDP, include the -o udp option to mount when mounting the NFS-exported file system on the client system.

There are three ways to configure an NFS file system export. On demand via the command line (client side), automatically via the /etc/fstab file (client side), and automatically via autofs configuration files, such as /etc/auto.master and /etc/auto.misc (server side with NIS).

TCP has better congestion control than UDP (which has none). On a very congested network, UDP packets are the first packets that are dropped. This means that if NFS is writing data (in 8K chunks) all of that 8K must be retransmitted over UDP. Because of TCP's reliability, only parts of that 8K data are transmitted at a time.

Error detection. When a TCP connection breaks (due to the server being unavailable) the client stops sending data and restarts the connection process once the server becomes available. With UDP, since it's connection-less, the client continues to pound the network with data until the server reestablishes a connection.

The main disadvantage is that there is a very small performance hit due to the overhead associated with the TCP protocol.

21.2.4. Preserving ACLs

The Red Hat Enterprise Linux 4 kernel provides ACL support for the ext3 file system and ext3 file systems mounted with the NFS or Samba protocols. Thus, if an ext3 file system has ACLs enabled for it and is NFS exported, and if the NFS client can read ACLs, they are used by the NFS client as well.

21.3. Exporting NFS File Systems

Sharing or serving files from an NFS server is known as exporting the directories. The NFS Server Configuration Tool can be used to configure a system as an NFS server.

To use the NFS Server Configuration Tool, you must be running the X Window System, have root privileges, and have the system-config-nfs RPM package installed. To start the application, select the Main Menu Button (on the Panel) => System Settings => Server Settings => NFS, or type the command system-config-nfs.

Basic permissions — Specify whether the directory should have read-only or read/write permissions.

Figure 21.2. Add Share

The General Options tab allows the following options to be configured:

Allow connections from port 1024 and higher — Services started on port numbers less than 1024 must be started as root. Select this option to allow the NFS service to be started by a user other than root. This option corresponds to insecure.

Allow insecure file locking — Do not require a lock request. This option corresponds to insecure_locks.

Disable subtree checking — If a subdirectory of a file system is exported, but the entire file system is not exported, the server checks to see if the requested file is in the subdirectory exported. This check is called subtree checking. Select this option to disable subtree checking. If the entire file system is exported, selecting to disable subtree checking can increase the transfer rate. This option corresponds to no_subtree_check.

Sync write operations on request — Enabled by default, this option does not allow the server to reply to requests before the changes made by the request are written to the disk. This option corresponds to sync. If this is not selected, the async option is used.

Force sync of write operations immediately — Do not delay writing to disk. This option corresponds to no_wdelay.

The User Access tab allows the following options to be configured:

Treat remote root user as local root — By default, the user and group IDs of the root user are both 0. Root squashing maps the user ID 0 and the group ID 0 to the user and group IDs of anonymous so that root on the client does not have root privileges on the NFS server. If this option is selected, root is not mapped to anonymous, and root on a client has root privileges to exported directories. Selecting this option can greatly decrease the security of the system. Do not select it unless it is absolutely necessary. This option corresponds to no_root_squash.

Treat all client users as anonymous users — If this option is selected, all user and group IDs are mapped to the anonymous user. This option corresponds to all_squash.

Specify local user ID for anonymous users — If Treat all client users as anonymous users is selected, this option lets you specify a user ID for the anonymous user. This option corresponds to anonuid.

Specify local group ID for anonymous users — If Treat all client users as anonymous users is selected, this option lets you specify a group ID for the anonymous user. This option corresponds to anongid.

To edit an existing NFS share, select the share from the list, and click the Properties button. To delete an existing NFS share, select the share from the list, and click the Delete button.

After clicking OK to add, edit, or delete an NFS share from the list, the changes take place immediately — the server daemon is restarted and the old configuration file is saved as /etc/exports.bak. The new configuration is written to /etc/exports.

The NFS Server Configuration Tool reads and writes directly to the /etc/exports configuration file. Thus, the file can be modified manually after using the tool, and the tool can be used after modifying the file manually (provided the file was modified with correct syntax).

21.3.1. Command Line Configuration

If you prefer editing configuration files using a text editor or if you do not have the X Window System installed, you can modify the configuration file directly.

The /etc/exports file controls what directories the NFS server exports. Its format is as follows:

directoryhostname(options)

The only option that needs to be specified is one of sync or async (sync is recommended). If sync is specified, the server does not reply to requests before the changes made by the request are written to the disk.

For example,

/misc/export speedy.example.com(sync)

would allow users from speedy.example.com to mount /misc/export with the default read-only permissions, but,

/misc/export speedy.example.com(rw,sync)

would allow users from speedy.example.com to mount /misc/export with read/write privileges.

Refer to the Reference Guide for a list of options that can be specified.

Warning

Be careful with spaces in the /etc/exports file. If there are no spaces between the hostname and the options in parentheses, the options apply only to the hostname. If there is a space between the hostname and the options, the options apply to the rest of the world. For example, examine the following lines:

The first line grants users from speedy.example.com read-write access and denies all other users. The second line grants users from speedy.example.com read-only access (the default) and allows the rest of the world read-write access.

Each time you change /etc/exports, you must inform the NFS daemon of the change, or reload the configuration file with the following command:

/sbin/service nfs reload

21.3.2. Hostname Formats

The host(s) can be in the following forms:

Single machine — A fully qualified domain name (that can be resolved by the server), hostname (that can be resolved by the server), or an IP address.

Series of machines specified with wildcards — Use the * or ? character to specify a string match. Wildcards are not to be used with IP addresses; however, they may accidentally work if reverse DNS lookups fail. When specifying wildcards in fully qualified domain names, dots (.) are not included in the wildcard. For example, *.example.com includes one.example.com but does not include one.two.example.com.

IP networks — Use a.b.c.d/z, where a.b.c.d is the network and z is the number of bits in the netmask (for example 192.168.0.0/24). Another acceptable format is a.b.c.d/netmask, where a.b.c.d is the network and netmask is the netmask (for example, 192.168.100.8/255.255.255.0).

Netgroups — In the format @group-name, where group-name is the NIS netgroup name.

21.3.3. Starting and Stopping the Server

On the server that is exporting NFS file systems, the nfs service must be running.

Samba uses the SMB protocol to share files and printers across a network connection. Operating systems that support this protocol include Microsoft Windows, OS/2, and Linux.

The Red Hat Enterprise Linux 4 kernel contains Access Control List (ACL) support for ext3 file systems. If the Samba server shares an ext3 file system with ACLs enabled for it, and the kernel on the client system contains support for reading ACLs from ext3 file systems, the client automatically recognizes and uses the ACLs. Refer to Chapter 14, Access Control Lists for more information on ACLs.

22.1. Why Use Samba?

Samba is useful if you have a network of both Windows and Linux machines. Samba allows files and printers to be shared by all the systems in a network. To share files between Linux machines only, use NFS as discussed in Chapter 21, Network File System (NFS). To share printers between Linux machines only, you do not need to use Samba; refer to Chapter 33, Printer Configuration.

22.2. Configuring a Samba Server

The default configuration file (/etc/samba/smb.conf) allows users to view their home directories as a Samba share. It also shares all printers configured for the system as Samba shared printers. In other words, you can attach a printer to the system and print to it from the Windows machines on your network.

22.2.1. Graphical Configuration

The Samba Server Configuration Tool is a graphical interface for managing Samba shares, users, and basic server settings. It modifies the configuration files in the /etc/samba/ directory. Any changes to these files not made using the application are preserved.

To use this application, you must be running the X Window System, have root privileges, and have the system-config-samba RPM package installed. To start the Samba Server Configuration Tool from the desktop, go to the Main Menu Button (on the Panel) => System Settings => Server Settings => Samba or type the command system-config-samba at a shell prompt (for example, in an XTerm or a GNOME terminal).

Figure 22.1. Samba Server Configuration Tool

Note

The Samba Server Configuration Tool does not display shared printers or the default stanza that allows users to view their own home directories on the Samba server.

22.2.1.1. Configuring Server Settings

The first step in configuring a Samba server is to configure the basic settings for the server and a few security options. After starting the application, select Preferences => Server Settings from the pulldown menu. The Basic tab is displayed as shown in Figure 22.2, “Configuring Basic Server Settings”.

Figure 22.2. Configuring Basic Server Settings

On the Basic tab, specify which workgroup the computer should be in as well as a brief description of the computer. They correspond to the workgroup and server string options in smb.conf.

Figure 22.3. Configuring Security Server Settings

The Security tab contains the following options:

Authentication Mode — This corresponds to the security option. Select one of the following types of authentication.

ADS — The Samba server acts as a domain member in an Active Directory Domain (ADS) realm. For this option, Kerberos must be installed and configured on the server, and Samba must become a member of the ADS realm using the net utility, which is part of the samba-client package. Refer to the net man page for details. This option does not configure Samba to be an ADS Controller. Specify the realm of the Kerberos server in the Kerberos Realm field.

Note

The Kerberos Realm field must be supplied in all uppercase letters, such as EXAMPLE.COM.

Use of your Samba server as a domain member in an ADS realm assumes proper configuration of Kerberos, including the /etc/krb5.conf file.

Domain — The Samba server relies on a Windows NT Primary or Backup Domain Controller to verify the user. The server passes the username and password to the Controller and waits for it to return. Specify the NetBIOS name of the Primary or Backup Domain Controller in the Authentication Server field.

The Encrypted Passwords option must be set to Yes if this is selected.

Server — The Samba server tries to verify the username and password combination by passing them to another Samba server. If it can not, the server tries to verify using the user authentication mode. Specify the NetBIOS name of the other Samba server in the Authentication Server field.

Share — Samba users do not have to enter a username and password combination on a per Samba server basis. They are not prompted for a username and password until they try to connect to a specific shared directory from a Samba server.

User — (Default) Samba users must provide a valid username and password on a per Samba server basis. Select this option if you want the Windows Username option to work. Refer to Section 22.2.1.2, “Managing Samba Users” for details.

Encrypt Passwords — This option must be enabled if the clients are connecting from a system with Windows 98, Windows NT 4.0 with Service Pack 3, or other more recent versions of Microsoft Windows. The passwords are transfered between the server and the client in an encrypted format instead of as a plain-text word that can be intercepted. This corresponds to the encrypted passwords option. Refer to Section 22.2.3, “Encrypted Passwords” for more information about encrypted Samba passwords.

Guest Account — When users or guest users log into a Samba server, they must be mapped to a valid user on the server. Select one of the existing usernames on the system to be the guest Samba account. When guests log in to the Samba server, they have the same privileges as this user. This corresponds to the guest account option.

After clicking OK, the changes are written to the configuration file and the daemon is restart; thus, the changes take effect immediately.

22.2.1.2. Managing Samba Users

The Samba Server Configuration Tool requires that an existing user account be active on the system acting as the Samba server before a Samba user can be added. The Samba user is associated with the existing user account.

Figure 22.4. Managing Samba Users

To add a Samba user, select Preferences => Samba Users from the pulldown menu, and click the Add User button. In the Create New Samba User window select a Unix Username from the list of existing users on the local system.

If the user has a different username on a Windows machine and needs to log into the Samba server from the Windows machine, specify that Windows username in the Windows Username field. The Authentication Mode on the Security tab of the Server Settings preferences must be set to User for this option to work.

Also configure a Samba Password for the Samba User and confirm it by typing it again. Even if you select to use encrypted passwords for Samba, it is recommended that the Samba passwords for all users are different from their system passwords.

To edit an existing user, select the user from the list, and click Edit User. To delete an existing Samba user, select the user, and click the Delete User button. Deleting a Samba user does not delete the associated system user account.

The users are modified immediately after clicking the OK button.

22.2.1.3. Adding a Share

To create a Samba share, click the Add button from the main Samba configuration window.

Figure 22.5. Adding a Share

The Basic tab configures the following options:

Directory — The directory to share via Samba. The directory must exist before it can be entered here.

Share name — The actual name of the share that is seen from remote machines. By default, it is the same value as Directory, but can be configured.

Descriptions — A brief description of the share.

Basic Permissions — Whether users should only be able to read the files in the shared directory or whether they should be able to read and write to the shared directory.

On the Access tab, select whether to allow only specified users to access the share or whether to allow all Samba users to access the share. If you select to allow access to specific users, select the users from the list of available Samba users.

The share is added immediately after clicking OK.

22.2.2. Command Line Configuration

Samba uses /etc/samba/smb.conf as its configuration file. If you change this configuration file, the changes do not take effect until you restart the Samba daemon with the command service smb restart.

To specify the Windows workgroup and a brief description of the Samba server, edit the following lines in your smb.conf file:

workgroup = WORKGROUPNAME
server string = BRIEF COMMENT ABOUT SERVER

Replace WORKGROUPNAME with the name of the Windows workgroup to which this machine should belong. The BRIEF COMMENT ABOUT SERVER is optional and is used as the Windows comment about the Samba system.

To create a Samba share directory on your Linux system, add the following section to your smb.conf file (after modifying it to reflect your needs and your system):

The above example allows the users tfox and carole to read and write to the directory /home/share, on the Samba server, from a Samba client.

22.2.3. Encrypted Passwords

Encrypted passwords are enabled by default because it is more secure. If encrypted passwords are not used, plain text passwords are used, which can be intercepted by someone using a network packet sniffer. It is recommended that encrypted passwords be used.

The Microsoft SMB Protocol originally used plain text passwords. However, Windows NT 4.0 with Service Pack 3 or higher, Windows 98, Windows 2000, Windows ME, and Windows XP require encrypted Samba passwords. To use Samba between a Linux system and a system running one of these Windows operating systems, you can either edit your Windows registry to use plaintext passwords or configure Samba on your Linux system to use encrypted passwords. If you choose to modify your registry, you must do so for all of your Windows machines — this is risky and may cause further conflicts. It is recommended that you use encrypted passwords for better security.

To configure Samba to use encrypted passwords, follow these steps:

Create a separate password file for Samba. To create one based on your existing /etc/passwd file, at a shell prompt, type the following command:

cat /etc/passwd | mksmbpasswd.sh > /etc/samba/smbpasswd

If the system uses NIS, type the following command:

ypcat passwd | mksmbpasswd.sh > /etc/samba/smbpasswd

The mksmbpasswd.sh script is installed in your /usr/bin directory with the samba package.

Change the permissions of the Samba password file so that only root has read and write permissions:

chmod 600 /etc/samba/smbpasswd

The script does not copy user passwords to the new file, and a Samba user account is not active until a password is set for it. For higher security, it is recommended that the user's Samba password be different from the user's system password. To set each Samba user's password, use the following command (replace username with each user's username):

smbpasswd username

Encrypted passwords must be enabled. Since they are enabled by default, they do not have to be specifically enabled in the configuration file. However, they can not be disabled in the configuration file either. In the file /etc/samba/smb.conf, verify that the following line does not exist:

encrypt passwords = no

If it does exist but is commented out with a semi-colon (;) at the beginning of the line, then the line is ignored, and encrypted passwords are enabled. If this line exists but is not commented out, either remove it or comment it out.

To specifically enable encrypted passwords in the configuration file, add the following lines to etc/samba/smb.conf:

encrypt passwords = yes
smb passwd file = /etc/samba/smbpasswd

Make sure the smb service is started by typing the command service smb restart at a shell prompt.

The pam_smbpass PAM module can be used to sync users' Samba passwords with their system passwords when the passwd command is used. If a user invokes the passwd command, the password he uses to log in to the Red Hat Enterprise Linux system as well as the password he must provide to connect to a Samba share are changed.

To enable this feature, add the following line to /etc/pam.d/system-auth below the pam_cracklib.so invocation:

To view active connections to the system, execute the command smbstatus.

22.3. Connecting to a Samba Share

You can use Nautilus to view available Samba shares on your network. Select Main Menu Button (on the Panel) => Network Servers to view a list of Samba workgroups on your network. You can also type smb: in the Location: bar of Nautilus to view the workgroups.

Double-click one of the workgroup icons to view a list of computers within the workgroup.

Figure 22.7. SMB Machines in Nautilus

As you can see from Figure 22.7, “SMB Machines in Nautilus”, there is an icon for each machine within the workgroup. Double-click on an icon to view the Samba shares on the machine. If a username and password combination is required, you are prompted for them.

Alternately, you can also specify the Samba server and sharename in the Location: bar for Nautilus using the following syntax (replace <servername> and <sharename> with the appropriate values):

smb://<servername>/<sharename>/

22.3.1. Command Line

To query the network for Samba servers, use the findsmb command. For each server found, it displays its IP address, NetBIOS name, workgroup name, operating system, and SMB server version.

To connect to a Samba share from a shell prompt, type the following command:

smbclient //<hostname>/<sharename> -U <username>

Replace <hostname> with the hostname or IP address of the Samba server you want to connect to, <sharename> with the name of the shared directory you want to browse, and <username> with the Samba username for the system. Enter the correct password or press Enter if no password is required for the user.

If you see the smb:\> prompt, you have successfully logged in. Once you are logged in, type help for a list of commands. If you wish to browse the contents of your home directory, replace sharename with your username. If the -U switch is not used, the username of the current user is passed to the Samba server.

To exit smbclient, type exit at the smb:\> prompt.

22.3.2. Mounting the Share

Sometimes it is useful to mount a Samba share to a directory so that the files in the directory can be treated as if they are part of the local file system.

To mount a Samba share to a directory, create the directory if it does not already exist, and execute the following command as root:

Dynamic Host Configuration Protocol (DHCP) is a network protocol for automatically assigning TCP/IP information to client machines. Each DHCP client connects to the centrally-located DHCP server which returns that client's network configuration, including the IP address, gateway, and DNS servers.

23.1. Why Use DHCP?

DHCP is useful for automatic configuration of client network interfaces. When configuring the client system, the administrator can choose DHCP and instead of entering an IP address, netmask, gateway, or DNS servers. The client retrieves this information from the DHCP server. DHCP is also useful if an administrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring all the systems, he can just edit one DHCP configuration file on the server for the new set of IP addresses. If the DNS servers for an organization changes, the changes are made on the DHCP server, not on the DHCP clients. Once the network is restarted on the clients (or the clients are rebooted), the changes take effect.

Furthermore, if a laptop or any type of mobile computer is configured for DHCP, it can be moved from office to office without being reconfigured as long as each office has a DHCP server that allows it to connect to the network.

23.2. Configuring a DHCP Server

To configure a DHCP server, the /etc/dhcpd.conf configuration file must be created. A sample file can be found at /usr/share/doc/dhcp-<version>/dhcpd.conf.sample.

23.2.1. Configuration File

The first step in configuring a DHCP server is to create the configuration file that stores the network information for the clients. Global options can be declared for all clients, while other options can be declared for individual client systems.

The configuration file can contain extra tabs or blank lines for easier formatting. Keywords are case-insensitive and lines beginning with a hash mark (#) are considered comments.

Two DNS update schemes are currently implemented — the ad-hoc DNS update mode and the interim DHCP-DNS interaction draft update mode. If and when these two are accepted as part of the Internet Engineering Task Force (IETF) standards process, there will be a third mode — the standard DNS update method. The DHCP server must be configured to use one of the two current schemes. Version 3.0b2pl11 and previous versions used the ad-hoc mode; however, it has been deprecated. To keep the same behavior, add the following line to the top of the configuration file:

ddns-update-style ad-hoc;

To use the recommended mode, add the following line to the top of the configuration file:

ddns-update-style interim;

Refer to the dhcpd.conf man page for details about the different modes.

There are two types of statements in the configuration file:

Parameters — State how to perform a task, whether to perform a task, or what network configuration options to send to the client.

Declarations — Describe the topology of the network, describe the clients, provide addresses for the clients, or apply a group of parameters to a group of declarations.

Some parameters must start with the option keyword and are referred to as options. Options configure DHCP options; whereas, parameters configure values that are not optional or control how the DHCP server behaves.

Parameters (including options) declared before a section enclosed in curly brackets ({ }) are considered global parameters. Global parameters apply to all the sections below it.

Important

If the configuration file is changed, the changes do not take effect until the DHCP daemon is restarted with the command service dhcpd restart.

Tip

Instead of changing a DHCP configuration file and restarting the service each time, using the omshell command provides an interactive way to connect to, query, and change the configuration of a DHCP server. By using omshell, all changes can be made while the server is running. For more information on omshell, refer to the omshell man page.

In Example 23.1, “Subnet Declaration”, the routers, subnet-mask, domain-name, domain-name-servers, and time-offset options are used for any host statements declared below it.

Additionally, a subnet can be declared, a subnet declaration must be included for every subnet in the network. If it is not, the DHCP server fails to start.

In this example, there are global options for every DHCP client in the subnet and a range declared. Clients are assigned an IP address within the range.

All subnets that share the same physical network should be declared within a shared-network declaration as shown in Example 23.2, “Shared-network Declaration”. Parameters within the shared-network, but outside the enclosed subnet declarations, are considered to be global parameters. The name of the shared-network should be a descriptive title for the network, such as using the title 'test-lab' to describe all the subnets in a test lab environment.

As demonstrated in Example 23.3, “Group Declaration”, the group declaration can be used to apply global parameters to a group of declarations. For example, shared networks, subnets, and hosts can be grouped.

To configure a DHCP server that leases a dynamic IP address to a system within a subnet, modify Example 23.4, “Range Parameter” with your values. It declares a default lease time, maximum lease time, and network configuration values for the clients. This example assigns IP addresses in the range 192.168.1.10 and 192.168.1.100 to client systems.

To assign an IP address to a client based on the MAC address of the network interface card, use the hardware ethernet parameter within a host declaration. As demonstrated in Example 23.5, “Static IP Address using DHCP”, the host apex declaration specifies that the network interface card with the MAC address 00:A0:78:8E:9E:AA always receives the IP address 192.168.1.4.

Note that the optional parameter host-name can also be used to assign a host name to the client.

For a complete list of option statements and what they do, refer to the dhcp-options man page.

23.2.2. Lease Database

On the DHCP server, the file /var/lib/dhcp/dhcpd.leases stores the DHCP client lease database. This file should not be modified by hand. DHCP lease information for each recently assigned IP address is automatically stored in the lease database. The information includes the length of the lease, to whom the IP address has been assigned, the start and end dates for the lease, and the MAC address of the network interface card that was used to retrieve the lease.

All times in the lease database are in Greenwich Mean Time (GMT), not local time.

The lease database is recreated from time to time so that it is not too large. First, all known leases are saved in a temporary lease database. The dhcpd.leases file is renamed dhcpd.leases~ and the temporary lease database is written to dhcpd.leases.

The DHCP daemon could be killed or the system could crash after the lease database has been renamed to the backup file but before the new file has been written. If this happens, the dhcpd.leases file does not exist, but it is required to start the service. Do not create a new lease file. If you do, all old leases are lost which causes many problems. The correct solution is to rename the dhcpd.leases~ backup file to dhcpd.leases and then start the daemon.

23.2.3. Starting and Stopping the Server

Important

When the DHCP server is started for the first time, it fails unless the dhcpd.leases file exists. Use the command touch /var/lib/dhcp/dhcpd.leases to create the file if it does not exist.

If the same server is also running BIND as a DNS server, this step is not necessary, as starting the named service automatically checks for a dhcpd.leases file.

To start the DHCP service, use the command /sbin/service dhcpd start. To stop the DHCP server, use the command /sbin/service dhcpd stop.

By default, the DHCP service does not start at boot time. To configure the daemon to start automatically at boot time, refer to Chapter 19, Controlling Access to Services for information on how to manage services.

If more than one network interface is attached to the system, but the DHCP server should only be started on one of the interfaces, configure the DHCP server to start only on that device. In /etc/sysconfig/dhcpd, add the name of the interface to the list of DHCPDARGS:

# Command line options here
DHCPDARGS=eth0

This is useful for a firewall machine with two network cards. One network card can be configured as a DHCP client to retrieve an IP address to the Internet. The other network card can be used as a DHCP server for the internal network behind the firewall. Specifying only the network card connected to the internal network makes the system more secure because users can not connect to the daemon via the Internet.

Other command line options that can be specified in /etc/sysconfig/dhcpd include:

-p <portnum> — Specify the UDP port number on which dhcpd should listen. The default is port 67. The DHCP server transmits responses to the DHCP clients at a port number one greater than the UDP port specified. For example, if the default port 67 is used, the server listens on port 67 for requests and responses to the client on port 68. If a port is specified here and the DHCP relay agent is used, the same port on which the DHCP relay agent should listen must be specified. Refer to Section 23.2.4, “DHCP Relay Agent” for details.

-f — Run the daemon as a foreground process. This is mostly used for debugging.

-d — Log the DHCP server daemon to the standard error descriptor. This is mostly used for debugging. If this is not specified, the log is written to /var/log/messages.

-cf <filename> — Specify the location of the configuration file. The default location is /etc/dhcpd.conf.

-lf <filename> — Specify the location of the lease database file. If a lease database file already exists, it is very important that the same file be used every time the DHCP server is started. It is strongly recommended that this option only be used for debugging purposes on non-production machines. The default location is /var/lib/dhcp/dhcpd.leases.

-q — Do not print the entire copyright message when starting the daemon.

23.2.4. DHCP Relay Agent

The DHCP Relay Agent (dhcrelay) allows for the relay of DHCP and BOOTP requests from a subnet with no DHCP server on it to one or more DHCP servers on other subnets.

When a DHCP client requests information, the DHCP Relay Agent forwards the request to the list of DHCP servers specified when the DHCP Relay Agent is started. When a DHCP server returns a reply, the reply is broadcast or unicast on the network that sent the original request.

The DHCP Relay Agent listens for DHCP requests on all interfaces unless the interfaces are specified in /etc/sysconfig/dhcrelay with the INTERFACES directive.

To start the DHCP Relay Agent, use the command service dhcrelay start.

23.3. Configuring a DHCP Client

The first step for configuring a DHCP client is to make sure the kernel recognizes the network interface card. Most cards are recognized during the installation process and the system is configured to use the correct kernel module for the card. If a card is added after installation, Kudzu[6] should recognize it and prompt for the configuration of the corresponding kernel module for it. Be sure to check the Hardware Compatibility List available at http://hardware.redhat.com/hcl/. If the network card is not configured by the installation program or Kudzu and you know which kernel module to load for it, refer to Chapter 37, Kernel Modules for details on loading kernel modules.

To configure a DHCP client manually, modify the /etc/sysconfig/network file to enable networking and the configuration file for each network device in the /etc/sysconfig/network-scripts directory. In this directory, each device should have a configuration file named ifcfg-eth0, where eth0 is the network device name.

The /etc/sysconfig/network file should contain the following line:

NETWORKING=yes

The NETWORKING variable must be set to yes if you want networking to start at boot time.

The /etc/sysconfig/network-scripts/ifcfg-eth0 file should contain the following lines:

DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes

A configuration file is needed for each device to be configured to use DHCP.

Other options for the network script include:

DHCP_HOSTNAME — Only use this option if the DHCP server requires the client to specify a hostname before receiving an IP address. (The DHCP server daemon in Red Hat Enterprise Linux does not support this feature.)

PEERDNS=<answer> , where <answer> is one of the following:

yes — Modify /etc/resolv.conf with information from the server. If using DHCP, then yes is the default.

no — Do not modify /etc/resolv.conf.

SRCADDR=<address> , where <address> is the specified source IP address for outgoing packets.

USERCTL=<answer> , where <answer> is one of the following:

yes — Non-root users are allowed to control this device.

no — Non-root users are not allowed to control this device.

If you prefer using a graphical interface, refer to Chapter 17, Network Configuration for details on using the Network Administration Tool to configure a network interface to use DHCP.

Tip

For advanced configurations of client DHCP options such as protocol timing, lease requirements and requests, dynamic DNS support, aliases, as well as a wide variety of values to override, prepend, or append to client-side configurations, refer to the dhclient and dhclient.conf man pages.

23.4. Additional Resources

For configuration options not covered here, refer to the following resources.

23.4.1. Installed Documentation

dhcpd man page — Describes how the DHCP daemon works.

dhcpd.conf man page — Explains how to configure the DHCP configuration file; includes some examples.

dhcpd.leases man page — Explains how to configure the DHCP leases file; includes some examples.

dhcp-options man page — Explains the syntax for declaring DHCP options in dhcpd.conf; includes some examples.

Red Hat Enterprise Linux provides version 2.0 of the Apache HTTP Server. If you want to migrate an existing configuration file by hand, refer to the migration guide at /usr/share/doc/httpd-<ver>/migration.html or the Reference Guide for details.

If you configured the Apache HTTP Server with the HTTP Configuration Tool in previous versions of Red Hat Enterprise Linux and then performed an upgrade, you can use the HTTP Configuration Tool to migrate the configuration file to the new format for version 2.0. Start the HTTP Configuration Tool, make any changes to the configuration, and save it. The configuration file saved will be compatible with version 2.0.

The httpd and system-config-httpd RPM packages need to be installed to use the HTTP Configuration Tool. It also requires the X Window System and root access. To start the application, go to the Main Menu Button => System Settings => Server Settings => HTTP or type the command system-config-httpd at a shell prompt (for example, in an XTerm or GNOME Terminal).

The HTTP Configuration Tool allows you to configure the /etc/httpd/conf/httpd.conf configuration file for the Apache HTTP Server. It does not use the old srm.conf or access.conf configuration files; leave them empty. Through the graphical interface, you can configure directives such as virtual hosts, logging attributes, and maximum number of connections.

Only modules provided with Red Hat Enterprise Linux can be configured with the HTTP Configuration Tool. If additional modules are installed, they can not be configured using this tool.

Warning

Do not edit the /etc/httpd/conf/httpd.conf configuration file by hand if you wish to use this tool. The HTTP Configuration Tool generates this file after you save your changes and exit the program. If you want to add additional modules or configuration options that are not available in HTTP Configuration Tool, you cannot use this tool.

The general steps for configuring the Apache HTTP Server using the HTTP Configuration Tool are as follows:

Configure the basic settings under the Main tab.

Click on the Virtual Hosts tab and configure the default settings.

Under the Virtual Hosts tab, configure the Default Virtual Host.

To serve more than one URL or virtual host, add any additional virtual hosts.

Configure the server settings under the Server tab.

Configure the connections settings under the Performance Tuning tab.

Copy all necessary files to the DocumentRoot and cgi-bin directories.

Exit the application and select to save your settings.

24.1. Basic Settings

Use the Main tab to configure the basic server settings.

Figure 24.1. Basic Settings

Enter a fully qualified domain name that you have the right to use in the Server Name text area. This option corresponds to the ServerName directive in httpd.conf. The ServerName directive sets the hostname of the Web server. It is used when creating redirection URLs. If you do not define a server name, the Web server attempts to resolve it from the IP address of the system. The server name does not have to be the domain name resolved from the IP address of the server. For example, you might set the server name to www.example.com while the server's real DNS name is foo.example.com.

Enter the email address of the person who maintains the Web server in the Webmaster email address text area. This option corresponds to the ServerAdmin directive in httpd.conf. If you configure the server's error pages to contain an email address, this email address is used so that users can report a problem to the server's administrator. The default value is root@localhost.

Use the Available Addresses area to define the ports on which the server accepts incoming requests. This option corresponds to the Listen directive in httpd.conf. By default, Red Hat configures the Apache HTTP Server to listen to port 80 for non-secure Web communications.

Click the Add button to define additional ports on which to accept requests. A window as shown in Figure 24.2, “Available Addresses” appears. Either choose the Listen to all addresses option to listen to all IP addresses on the defined port or specify a particular IP address over which the server accepts connections in the Address field. Only specify one IP address per port number. To specify more than one IP address with the same port number, create an entry for each IP address. If at all possible, use an IP address instead of a domain name to prevent a DNS lookup failure. Refer to http://httpd.apache.org/docs-2.0/dns-caveats.html for more information about Issues Regarding DNS and Apache.

Entering an asterisk (*) in the Address field is the same as choosing Listen to all addresses. Clicking the Edit button in the Available Addresses frame shows the same window as the Add button except with the fields populated for the selected entry. To delete an entry, select it and click the Delete button.

Tip

If you set the server to listen to a port under 1024, you must be root to start it. For port 1024 and above, httpd can be started as a regular user.

Figure 24.2. Available Addresses

24.2. Default Settings

After defining the Server Name, Webmaster email address, and Available Addresses, click the Virtual Hosts tab and click the Edit Default Settings button. A window as shown in Figure 24.3, “Site Configuration” appears. Configure the default settings for your Web server in this window. If you add a virtual host, the settings you configure for the virtual host take precedence for that virtual host. For a directive not defined within the virtual host settings, the default value is used.

24.2.1. Site Configuration

The default values for the Directory Page Search List and Error Pages work for most servers. If you are unsure of these settings, do not modify them.

Figure 24.3. Site Configuration

The entries listed in the Directory Page Search List define the DirectoryIndex directive. The DirectoryIndex is the default page served by the server when a user requests an index of a directory by specifying a forward slash (/) at the end of the directory name.

For example, when a user requests the page http://www.example.com/this_directory/, they are going to get either the DirectoryIndex page, if it exists, or a server-generated directory list. The server tries to find one of the files listed in the DirectoryIndex directive and returns the first one it finds. If it does not find any of these files and if Options Indexes is set for that directory, the server generates and returns a list, in HTML format, of the subdirectories and files in the directory.

Use the Error Code section to configure Apache HTTP Server to redirect the client to a local or external URL in the event of a problem or error. This option corresponds to the ErrorDocument directive. If a problem or error occurs when a client tries to connect to the Apache HTTP Server, the default action is to display the short error message shown in the Error Code column. To override this default configuration, select the error code and click the Edit button. Choose Default to display the default short error message. Choose URL to redirect the client to an external URL and enter a complete URL, including the http://, in the Location field. Choose File to redirect the client to an internal URL and enter a file location under the document root for the Web server. The location must begin the a slash (/) and be relative to the Document Root.

For example, to redirect a 404 Not Found error code to a webpage that you created in a file called 404.html, copy 404.html to DocumentRoot/../error/404.html. In this case, DocumentRoot is the Document Root directory that you have defined (the default is /var/www/html/). If the Document Root is left as the default location, the file should be copied to /var/www/error/404.html. Then, choose File as the Behavior for 404 - Not Found error code and enter /error/404.html as the Location.

From the Default Error Page Footer menu, you can choose one of the following options:

Show footer with email address — Display the default footer at the bottom of all error pages along with the email address of the website maintainer specified by the ServerAdmin directive. Refer to Section 24.3.1.1, “General Options” for information about configuring the ServerAdmin directive.

Show footer — Display just the default footer at the bottom of error pages.

No footer — Do not display a footer at the bottom of error pages.

24.2.2. Logging

Use the Logging tab to configure options for specific transfer and error logs.

By default, the server writes the transfer log to the /var/log/httpd/access_log file and the error log to the /var/log/httpd/error_log file.

The transfer log contains a list of all attempts to access the Web server. It records the IP address of the client that is attempting to connect, the date and time of the attempt, and the file on the Web server that it is trying to retrieve. Enter the name of the path and file in which to store this information. If the path and file name do not start with a slash (/), the path is relative to the server root directory as configured. This option corresponds to the TransferLog directive.

The error log contains a list of any server errors that occur. Enter the name of the path and file in which to store this information. If the path and file name do not start with a slash (/), the path is relative to the server root directory as configured. This option corresponds to the ErrorLog directive.

Use the Log Level menu to set the verbosity of the error messages in the error logs. It can be set (from least verbose to most verbose) to emerg, alert, crit, error, warn, notice, info or debug. This option corresponds to the LogLevel directive.

If you choose Reverse Lookup, your server automatically resolves the IP address for each connection which requests a document from your Web server. Resolving the IP address means that your server makes one or more connections to the DNS in order to find out the hostname that corresponds to a particular IP address.

If you choose Double Reverse Lookup, your server performs a double-reverse DNS. In other words, after a reverse lookup is performed, a forward lookup is performed on the result. At least one of the IP addresses in the forward lookup must match the address from the first reverse lookup.

Generally, you should leave this option set to No Reverse Lookup, because the DNS requests add a load to your server and may slow it down. If your server is busy, the effects of trying to perform these reverse lookups or double reverse lookups may be quite noticeable.

Reverse lookups and double reverse lookups are also an issue for the Internet as a whole. Each individual connection made to look up each hostname adds up. Therefore, for your own Web server's benefit, as well as for the Internet's benefit, you should leave this option set to No Reverse Lookup.

24.2.3. Environment Variables

Use the Environment tab to configure options for specific variables to set, pass, or unset for CGI scripts.

Sometimes it is necessary to modify environment variables for CGI scripts or server-side include (SSI) pages. The Apache HTTP Server can use the mod_env module to configure the environment variables which are passed to CGI scripts and SSI pages. Use the Environment Variables page to configure the directives for this module.

Use the Set for CGI Scripts section to set an environment variable that is passed to CGI scripts and SSI pages. For example, to set the environment variable MAXNUM to 50, click the Add button inside the Set for CGI Script section, as shown in Figure 24.5, “Environment Variables”, and type MAXNUM in the Environment Variable text field and 50 in the Value to set text field. Click OK to add it to the list. The Set for CGI Scripts section configures the SetEnv directive.

Use the Pass to CGI Scripts section to pass the value of an environment variable when the server is first started to CGI scripts. To see this environment variable, type the command env at a shell prompt. Click the Add button inside the Pass to CGI Scripts section and enter the name of the environment variable in the resulting dialog box. Click OK to add it to the list. The Pass to CGI Scripts section configures the PassEnv directive.

Figure 24.5. Environment Variables

To remove an environment variable so that the value is not passed to CGI scripts and SSI pages, use the Unset for CGI Scripts section. Click Add in the Unset for CGI Scripts section, and enter the name of the environment variable to unset. Click OK to add it to the list. This corresponds to the UnsetEnv directive.

To edit any of these environment values, select it from the list and click the corresponding Edit button. To delete any entry from the list, select it and click the corresponding Delete button.

To learn more about environment variables in the Apache HTTP Server, refer to the following:

24.2.4. Directories

Use the Directories page in the Performance tab to configure options for specific directories. This corresponds to the <Directory> directive.

Figure 24.6. Directories

Click the Edit button in the top right-hand corner to configure the Default Directory Options for all directories that are not specified in the Directory list below it. The options that you choose are listed as the Options directive within the <Directory> directive. You can configure the following options:

ExecCGI — Allow execution of CGI scripts. CGI scripts are not executed if this option is not chosen.

Indexes — Display a formatted list of the directory's contents, if no DirectoryIndex (such as index.html) exists in the requested directory.

Multiview — Support content-negotiated multiviews; this option is disabled by default.

SymLinksIfOwnerMatch — Only follow symbolic links if the target file or directory has the same owner as the link.

To specify options for specific directories, click the Add button beside the Directory list box. A window as shown in Figure 24.7, “Directory Settings” appears. Enter the directory to configure in the Directory text field at the bottom of the window. Select the options in the right-hand list and configure the Order directive with the left-hand side options. The Order directive controls the order in which allow and deny directives are evaluated. In the Allow hosts from and Deny hosts from text field, you can specify one of the following:

Allow all hosts — Type all to allow access to all hosts.

Partial domain name — Allow all hosts whose names match or end with the specified string.

Full IP address — Allow access to a specific IP address.

A subnet — Such as 192.168.1.0/255.255.255.0

A network CIDR specification — such as 10.3.0.0/16

Figure 24.7. Directory Settings

If you check the Let .htaccess files override directory options, the configuration directives in the .htaccess file take precedence.

24.3. Virtual Hosts Settings

Virtual hosts allow you to run different servers for different IP addresses, different host names, or different ports on the same machine. For example, you can run the website for http://www.example.com and http://www.anotherexample.com on the same Web server using virtual hosts. This option corresponds to the <VirtualHost> directive for the default virtual host and IP based virtual hosts. It corresponds to the <NameVirtualHost> directive for a name based virtual host.

The directives set for a virtual host only apply to that particular virtual host. If a directive is set server-wide using the Edit Default Settings button and not defined within the virtual host settings, the default setting is used. For example, you can define a Webmaster email address in the Main tab and not define individual email addresses for each virtual host.

24.3.1. Adding and Editing a Virtual Host

To add a virtual host, click the Virtual Hosts tab and then click the Add button. You can also edit a virtual host by selecting it and clicking the Edit button.

24.3.1.1. General Options

The General Options settings only apply to the virtual host that you are configuring. Set the name of the virtual host in the Virtual Host Name text area. This name is used by HTTP Configuration Tool to distinguish between virtual hosts.

Set the Document Root Directory value to the directory that contains the root document (such as index.html) for the virtual host. This option corresponds to the DocumentRoot directive within the <VirtualHost> directive. The default DocumentRoot is /var/www/html.

The Webmaster email address corresponds to the ServerAdmin directive within the VirtualHost directive. This email address is used in the footer of error pages if you choose to show a footer with an email address on the error pages.

In the Host Information section, choose Default Virtual Host, IP based Virtual Host, or Name based Virtual Host.

Default Virtual Host

You should only configure one default virtual host (remember that there is one setup by default). The default virtual host settings are used when the requested IP address is not explicitly listed in another virtual host. If there is no default virtual host defined, the main server settings are used.

IP based Virtual Host

If you choose IP based Virtual Host, a window appears to configure the <VirtualHost> directive based on the IP address of the server. Specify this IP address in the IP address field. To specify multiple IP addresses, separate each IP address with spaces. To specify a port, use the syntax IP Address:Port. Use "colon, asterisk" (:*) to configure all ports for the IP address. Specify the host name for the virtual host in the Server Host Name field.

Name based Virtual Host

If you choose Name based Virtual Host, a window appears to configure the NameVirtualHost directive based on the host name of the server. Specify the IP address in the IP address field. To specify multiple IP addresses, separate each IP address with spaces. To specify a port, use the syntax IP Address:Port. Use "colon, asterisk" (:*) to configure all ports for the IP address. Specify the host name for the virtual host in the Server Host Name field. In the Aliases section, click Add to add a host name alias. Adding an alias here adds a ServerAlias directive within the NameVirtualHost directive.

24.3.1.2. SSL

Note

You cannot use name based virtual hosts with SSL because the SSL handshake (when the browser accepts the secure Web server's certificate) occurs before the HTTP request, which identifies the appropriate name based virtual host. If you plan to use name-based virtual hosts, remember that they only work with your non-secure Web server.

Figure 24.9. SSL Support

If an Apache HTTP Server is not configured with SSL support, communications between an Apache HTTP Server and its clients are not encrypted. This is appropriate for websites without personal or confidential information. For example, an open source website that distributes open source software and documentation has no need for secure communications. However, an ecommerce website that requires credit card information should use the Apache SSL support to encrypt its communications. Enabling Apache SSL support enables the use of the mod_ssl security module. To enable it through the HTTP Configuration Tool, you must allow access through port 443 under the Main tab => Available Addresses. Refer to Section 24.1, “Basic Settings” for details. Then, select the virtual host name in the Virtual Hosts tab, click the Edit button, choose SSL from the left-hand menu, and check the Enable SSL Support option as shown in Figure 24.9, “SSL Support”. The SSL Configuration section is pre-configured with the dummy digital certificate. The digital certificate provides authentication for your secure Web server and identifies the secure server to client Web browsers. You must purchase your own digital certificate. Do not use the dummy one provided for your website. For details on purchasing a CA-approved digital certificate, refer to the Chapter 25, Apache HTTP Secure Server Configuration.

24.3.1.3. Additional Virtual Host Options

The Site Configuration, Environment Variables, and Directories options for the virtual hosts are the same directives that you set when you clicked the Edit Default Settings button, except the options set here are for the individual virtual hosts that you are configuring. Refer to Section 24.2, “Default Settings” for details on these options.

24.4. Server Settings

The Server tab allows you to configure basic server settings. The default settings for these options are appropriate for most situations.

Figure 24.10. Server Configuration

The Lock File value corresponds to the LockFile directive. This directive sets the path to the lockfile used when the server is compiled with either USE_FCNTL_SERIALIZED_ACCEPT or USE_FLOCK_SERIALIZED_ACCEPT. It must be stored on the local disk. It should be left to the default value unless the logs directory is located on an NFS share. If this is the case, the default value should be changed to a location on the local disk and to a directory that is readable only by root.

The PID File value corresponds to the PidFile directive. This directive sets the file in which the server records its process ID (pid). This file should only be readable by root. In most cases, it should be left to the default value.

The Core Dump Directory value corresponds to the CoreDumpDirectory directive. The Apache HTTP Server tries to switch to this directory before executing a core dump. The default value is the ServerRoot. However, if the user that the server runs as can not write to this directory, the core dump can not be written. Change this value to a directory writable by the user the server runs as, if you want to write the core dumps to disk for debugging purposes.

The User value corresponds to the User directive. It sets the userid used by the server to answer requests. This user's settings determine the server's access. Any files inaccessible to this user are also inaccessible to your website's visitors. The default for User is apache.

The user should only have privileges so that it can access files which are supposed to be visible to the outside world. The user is also the owner of any CGI processes spawned by the server. The user should not be allowed to execute any code which is not intended to be in response to HTTP requests.

Warning

Unless you know exactly what you are doing, do not set the User directive to root. Using root as the User creates large security holes for your Web server.

The parent httpd process first runs as root during normal operations, but is then immediately handed off to the apache user. The server must start as root because it needs to bind to a port below 1024. Ports below 1024 are reserved for system use, so they can not be used by anyone but root. Once the server has attached itself to its port, however, it hands the process off to the apache user before it accepts any connection requests.

The Group value corresponds to the Group directive. The Group directive is similar to the User directive. Group sets the group under which the server answers requests. The default group is also apache.

24.5. Performance Tuning

Click on the Performance Tuning tab to configure the maximum number of child server processes you want and to configure the Apache HTTP Server options for client connections. The default settings for these options are appropriate for most situations. Altering these settings may affect the overall performance of your Web server.

Figure 24.11. Performance Tuning

Set Max Number of Connections to the maximum number of simultaneous client requests that the server can handle. For each connection, a child httpd process is created. After this maximum number of processes is reached, no one else can connect to the Web server until a child server process is freed. You can not set this value to higher than 256 without recompiling. This option corresponds to the MaxClients directive.

Connection Timeout defines, in seconds, the amount of time that your server waits for receipts and transmissions during communications. Specifically, Connection Timeout defines how long your server waits to receive a GET request, how long it waits to receive TCP packets on a POST or PUT request, and how long it waits between ACKs responding to TCP packets. By default, Connection Timeout is set to 300 seconds, which is appropriate for most situations. This option corresponds to the TimeOut directive.

Set the Max requests per connection to the maximum number of requests allowed per persistent connection. The default value is 100, which should be appropriate for most situations. This option corresponds to the MaxRequestsPerChild directive.

If you check the Allow unlimited requests per connection option, the MaxKeepAliveRequests directive is set to 0 and unlimited requests are allowed.

If you uncheck the Allow Persistent Connections option, the KeepAlive directive is set to false. If you check it, the KeepAlive directive is set to true, and the KeepAliveTimeout directive is set to the number that is selected as the Timeout for next Connection value. This directive sets the number of seconds your server waits for a subsequent request, after a request has been served, before it closes the connection. Once a request has been received, the Connection Timeout value applies instead.

Setting the Persistent Connections to a high value may cause the server to slow down, depending on how many users are trying to connect to it. The higher the number, the more server processes are waiting for another connection from the last client that connected to it.

24.6. Saving Your Settings

If you do not want to save your Apache HTTP Server configuration settings, click the Cancel button in the bottom right corner of the HTTP Configuration Tool window. You are prompted to confirm this decision. If you click Yes to confirm this choice, your settings are not saved.

If you want to save your Apache HTTP Server configuration settings, click the OK button in the bottom right corner of the HTTP Configuration Tool window. A dialog window appears. If you answer Yes, your settings are saved in /etc/httpd/conf/httpd.conf. Remember that your original configuration file is overwritten with your new settings.

If this is the first time that you have used the HTTP Configuration Tool, a dialog window appears, warning you that the configuration file has been manually modified. If the HTTP Configuration Tool detects that the httpd.conf configuration file has been manually modified, it saves the manually modified file as /etc/httpd/conf/httpd.conf.bak.

Important

After saving your settings, you must restart the httpd daemon with the command service httpd restart. You must be logged in as root to execute this command.

24.7. Additional Resources

To learn more about the Apache HTTP Server, refer to the following resources.

24.7.1. Installed Documentation

/usr/share/docs/httpd-<version>/migration.html — The Apache Migration HOWTO document contains a list of changes from version 1.3 to version 2.0 as well as information about how to migration the configuration file manually.

25.1. Introduction

This chapter provides basic information on the Apache HTTP Server with the mod_ssl security module enabled to use the OpenSSL library and toolkit. The combination of these three components are referred to in this chapter as the secure Web server or just as the secure server.

The mod_ssl module is a security module for the Apache HTTP Server. The mod_ssl module uses the tools provided by the OpenSSL Project to add a very important feature to the Apache HTTP Server — the ability to encrypt communications. In contrast, regular HTTP communications between a browser and a Web server are sent in plain text, which could be intercepted and read by someone along the route between the browser and the server.

This chapter is not meant to be complete and exclusive documentation for any of these programs. When possible, this guide points to appropriate places where you can find more in-depth documentation on particular subjects.

This chapter shows you how to install these programs. You can also learn the steps necessary to generate a private key and a certificate request, how to generate your own self-signed certificate, and how to install a certificate to use with your secure server.

The mod_ssl configuration file is located at /etc/httpd/conf.d/ssl.conf. For this file to be loaded, and hence for mod_ssl to work, you must have the statement Include conf.d/*.conf in the /etc/httpd/conf/httpd.conf file. This statement is included by default in the default Apache HTTP Server configuration file.

25.2. An Overview of Security-Related Packages

To enable the secure server, you must have the following packages installed at a minimum:

The openssl package contains the OpenSSL toolkit. The OpenSSL toolkit implements the SSL and TLS protocols, and also includes a general purpose cryptography library.

Additionally, other software packages provide certain security functionalities (but are not required by the secure server to function):

httpd-devel

The httpd-devel package contains the Apache HTTP Server include files, header files, and the APXS utility. You need all of these if you intend to load any extra modules, other than the modules provided with this product. Refer to the Reference Guide for more information on loading modules onto your secure server using Apache's dynamic shared object (DSO) functionality.

If you do not intend to load other modules onto your Apache HTTP Server, you do not need to install this package.

OpenSSH packages

The OpenSSH packages provide the OpenSSH set of network connectivity tools for logging into and executing commands on a remote machine. OpenSSH tools encrypt all traffic (including passwords), so you can avoid eavesdropping, connection hijacking, and other attacks on the communications between your machine and the remote machine.

The openssh package includes core files needed by both the OpenSSH client programs and the OpenSSH server. The openssh package also contains scp, a secure replacement for rcp (for securely copying files between machines).

The openssh-askpass package supports the display of a dialog window which prompts for a password during use of the OpenSSH agent.

The openssh-askpass-gnome package can be used in conjunction with the GNOME desktop environment to display a graphical dialog window when OpenSSH programs prompt for a password. If you are running GNOME and using OpenSSH utilities, you should install this package.

The openssh-server package contains the sshd secure shell daemon and related files. The secure shell daemon is the server side of the OpenSSH suite and must be installed on your host to allow SSH clients to connect to your host.

The openssh-clients package contains the client programs needed to make encrypted connections to SSH servers, including the following: ssh, a secure replacement for rsh; sftp, a secure replacement for ftp (for transferring files between machines); and slogin, a secure replacement for rlogin (for remote login) and telnet (for communicating with another host via the Telnet protocol).

The openssl-devel package contains the static libraries and the include file needed to compile applications with support for various cryptographic algorithms and protocols. You need to install this package only if you are developing applications which include SSL support — you do not need this package to use SSL.

stunnel

The stunnel package provides the Stunnel SSL wrapper. Stunnel supports the SSL encryption of TCP connections. It provides encryption for non-SSL aware daemons and protocols (such as POP, IMAP, and LDAP) without requiring any changes to the daemon's code.

Note

Newer implementations of various daemons now provide their services natively over SSL, such as dovecot or OpenLDAP's slapd server, which may be more desirable than using stunnel.

For example, use of stunnel only provides wrapping of protocols, while the native support in OpenLDAP's slapd can also handle in-band upgrades for using encryption in response to a StartTLS client request.

Table 25.1, “Security Packages” displays a summary of the secure server packages and whether each package is optional for the installation of a secure server.

Table 25.1. Security Packages

Package Name

Optional?

httpd

no

mod_ssl

no

openssl

no

httpd-devel

yes

openssh

yes

openssh-askpass

yes

openssh-askpass-gnome

yes

openssh-clients

yes

openssh-server

yes

openssl-devel

yes

stunnel

yes

25.3. An Overview of Certificates and Security

Your secure server provides security using a combination of the Secure Sockets Layer (SSL) protocol and (in most cases) a digital certificate from a Certificate Authority (CA). SSL handles the encrypted communications as well as the mutual authentication between browsers and your secure server. The CA-approved digital certificate provides authentication for your secure server (the CA puts its reputation behind its certification of your organization's identity). When your browser is communicating using SSL encryption, the https:// prefix is used at the beginning of the Uniform Resource Locator (URL) in the navigation bar.

Encryption depends upon the use of keys (think of them as secret encoder/decoder rings in data format). In conventional or symmetric cryptography, both ends of the transaction have the same key, which they use to decode each other's transmissions. In public or asymmetric cryptography, two keys co-exist: a public key and a private key. A person or an organization keeps their private key a secret and publishes their public key. Data encoded with the public key can only be decoded with the private key; data encoded with the private key can only be decoded with the public key.

To set up your secure server, use public cryptography to create a public and private key pair. In most cases, you send your certificate request (including your public key), proof of your company's identity, and payment to a CA. The CA verifies the certificate request and your identity, and then sends back a certificate for your secure server.

A secure server uses a certificate to identify itself to Web browsers. You can generate your own certificate (called a "self-signed" certificate), or you can get a certificate from a CA. A certificate from a reputable CA guarantees that a website is associated with a particular company or organization.

Alternatively, you can create your own self-signed certificate. Note, however, that self-signed certificates should not be used in most production environments. Self-signed certificates are not automatically accepted by a user's browser — users are prompted by the browser to accept the certificate and create the secure connection. Refer to Section 25.5, “Types of Certificates” for more information on the differences between self-signed and CA-signed certificates.

Once you have a self-signed certificate or a signed certificate from the CA of your choice, you must install it on your secure server.

25.4. Using Pre-Existing Keys and Certificates

If you already have an existing key and certificate (for example, if you are installing the secure server to replace another company's secure server product), you can probably use your existing key and certificate with the secure server. The following two situations provide instances where you are not able to use your existing key and certificate:

If you are changing your IP address or domain name — Certificates are issued for a particular IP address and domain name pair. You must get a new certificate if you are changing your IP address or domain name.

If you have a certificate from VeriSign and you are changing your server software — VeriSign is a widely used CA. If you already have a VeriSign certificate for another purpose, you may have been considering using your existing VeriSign certificate with your new secure server. However, you are not be allowed to because VeriSign issues certificates for one specific server software and IP address/domain name combination.

If you change either of those parameters (for example, if you previously used a different secure server product), the VeriSign certificate you obtained to use with the previous configuration will not work with the new configuration. You must obtain a new certificate.

If you have an existing key and certificate that you can use, you do not have to generate a new key and obtain a new certificate. However, you may need to move and rename the files which contain your key and certificate.

If you are upgrading from the Red Hat Secure Web Server, your old key (httpsd.key) and certificate (httpsd.crt) are located in /etc/httpd/conf/. Move and rename your key and certificate so that the secure server can use them. Use the following two commands to move and rename your key and certificate files:

You are prompted to enter your passphrase. After you type it in and press Enter, the server starts.

25.5. Types of Certificates

If you installed your secure server from the RPM package provided by Red Hat, a random key and a test certificate are generated and put into the appropriate directories. Before you begin using your secure server, however, you must generate your own key and obtain a certificate which correctly identifies your server.

You need a key and a certificate to operate your secure server — which means that you can either generate a self-signed certificate or purchase a CA-signed certificate from a CA. What are the differences between the two?

A CA-signed certificate provides two important capabilities for your server:

Browsers (usually) automatically recognize the certificate and allow a secure connection to be made, without prompting the user.

When a CA issues a signed certificate, they are guaranteeing the identity of the organization that is providing the webpages to the browser.

If your secure server is being accessed by the public at large, your secure server needs a certificate signed by a CA so that people who visit your website know that the website is owned by the organization who claims to own it. Before signing a certificate, a CA verifies that the organization requesting the certificate was actually who they claimed to be.

Most Web browsers that support SSL have a list of CAs whose certificates they automatically accept. If a browser encounters a certificate whose authorizing CA is not in the list, the browser asks the user to either accept or decline the connection.

You can generate a self-signed certificate for your secure server, but be aware that a self-signed certificate does not provide the same functionality as a CA-signed certificate. A self-signed certificate is not automatically recognized by most Web browsers and does not provide any guarantee concerning the identity of the organization that is providing the website. A CA-signed certificate provides both of these important capabilities for a secure server. If your secure server is to be used in a production environment, a CA-signed certificate is recommended.

The process of getting a certificate from a CA is fairly easy. A quick overview is as follows:

Create an encryption private and public key pair.

Create a certificate request based on the public key. The certificate request contains information about your server and the company hosting it.

Send the certificate request, along with documents proving your identity, to a CA. Red Hat does not make recommendations on which certificate authority to choose. Your decision may be based on your past experiences, on the experiences of your friends or colleagues, or purely on monetary factors.

Once you have decided upon a CA, you need to follow the instructions they provide on how to obtain a certificate from them.

When the CA is satisfied that you are indeed who you claim to be, they provide you with a digital certificate.

You now must enter in a passphrase. For security reason, it should contain at least eight characters, include numbers and/or punctuation, and it should not be a word in a dictionary. Also, remember that your passphrase is case sensitive.

Note

You are required to remember and enter this passphrase every time you start your secure server. If you forget this passphrase, the key must be completely re-generated.

Re-type the passphrase to verify that it is correct. Once you have typed it in correctly, /etc/httpd/conf/ssl.key/server.key, the file containing your key, is created.

Note that if you do not want to type in a passphrase every time you start your secure server, you must use the following two commands instead of make genkey to create the key.

Use the following command to create your key:

/usr/bin/openssl genrsa 1024 > /etc/httpd/conf/ssl.key/server.key

Then, use the following command to make sure the permissions are set correctly for the file:

chmod go-rwx /etc/httpd/conf/ssl.key/server.key

After you use the above commands to create your key, you do not need to use a passphrase to start your secure server.

Warning

Disabling the passphrase feature for your secure server is a security risk. It is not recommended that you disable the passphrase feature for secure server.

Problems associated with not using a passphrase are directly related to the security maintained on the host machine. For example, if an unscrupulous individual compromises the regular UNIX security on the host machine, that person could obtain your private key (the contents of your server.key file). The key could be used to serve webpages that appear to be from your secure server.

If UNIX security practices are rigorously maintained on the host computer (all operating system patches and updates are installed as soon as they are available, no unnecessary or risky services are operating, and so on), secure server's passphrase may seem unnecessary. However, since your secure server should not need to be re-booted very often, the extra security provided by entering a passphrase is a worthwhile effort in most cases.

The server.key file should be owned by the root user on your system and should not be accessible to any other user. Make a backup copy of this file and keep the backup copy in a safe, secure place. You need the backup copy because if you ever lose the server.key file after using it to create your certificate request, your certificate no longer works and the CA is not able to help you. Your only option is to request (and pay for) a new certificate.

25.7. Generating a Certificate Request to Send to a CA

Once you have created a key, the next step is to generate a certificate request which you need to send to the CA of your choice. Make sure you are in the /usr/share/ssl/certs/ directory, and type the following command:

make certreq

Your system displays the following output and asks you for your passphrase (unless you disabled the passphrase option):

Type in the passphrase that you chose when you were generating your key unless you don't need to. Next, your system displays some instructions and then ask for a series of responses from you. Your inputs are incorporated into the certificate request. The display, with example responses, looks similar to the following:

You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a
DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [GB]:USState or Province Name (full name) [Berkshire]:North CarolinaLocality Name (eg, city) [Newbury]:RaleighOrganization Name (eg, company) [My Company Ltd]:Test CompanyOrganizational Unit Name (eg, section) []:TestingCommon Name (your name or server's hostname) []:test.example.comEmail Address []:admin@example.comPlease enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

The default answers appear in brackets ([]) immediately after each request for input. For example, the first information required is the name of the country where the certificate is to be used, shown like the following:

Country Name (2 letter code) [GB]:

The default input, in brackets, is GB. Accept the default by pressing Enter or fill in your country's two letter code.

You have to type in the rest of the values. All of these should be self-explanatory, but you must follow these guidelines:

Do not abbreviate the locality or state. Write them out (for example, St. Louis should be written out as Saint Louis).

If you are sending this CSR to a CA, be very careful to provide correct information for all of the fields, but especially for the Organization Name and the Common Name. CAs check the information provided in the CSR to determine whether your organization is responsible for what you provided as the Common Name. CAs rejects CSRs which include information they perceive as invalid.

For Common Name, make sure you type in the real name of your secure server (a valid DNS name) and not any aliases which the server may have.

The Email Address should be the email address for the webmaster or system administrator.

Avoid special characters like @, #, & !, and etc. Some CAs reject a certificate request which contains a special character. If your company name includes an ampersand (&), spell it out as "and" instead of "&."

Do not use either of the extra attributes (A challenge password and An optional company name). To continue without entering these fields, just press Enter to accept the blank default for both inputs.

The file /etc/httpd/conf/ssl.csr/server.csr is created when you have finished entering your information. This file is your certificate request, ready to send to your CA.

After you have decided on a CA, follow the instructions they provide on their website. Their instructions tell you how to send your certificate request, any other documentation that they require, and your payment to them.

After you have fulfilled the CA's requirements, they send a certificate to you (usually by email). Save (or cut and paste) the certificate that they send you as /etc/httpd/conf/ssl.crt/server.crt. Be sure to keep a backup of this file.

25.8. Creating a Self-Signed Certificate

You can create your own self-signed certificate. Note that a self-signed certificate does not provide the security guarantees of a CA-signed certificate. Refer to Section 25.5, “Types of Certificates” for more details about certificates.

To make your own self-signed certificate, first create a random key using the instructions provided in Section 25.6, “Generating a Key”. Once you have a key, make sure you are in the /usr/share/ssl/certs/ directory, and type the following command:

make testcert

The following output is shown and you are prompted for your passphrase (unless you generated a key without a passphrase):

Next, you are asked for more information. The computer's output and a set of inputs looks like the following (provide the correct information for your organization and host):

You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a
DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [GB]:US
State or Province Name (full name) [Berkshire]:North CarolinaLocality Name (eg, city) [Newbury]:RaleighOrganization Name (eg, company) [My Company Ltd]:My Company, Inc.Organizational Unit Name (eg, section) []:DocumentationCommon Name (your name or server's hostname) []:myhost.example.comEmail Address []:myemail@example.com

After you provide the correct information, a self-signed certificate is created in /etc/httpd/conf/ssl.crt/server.crt. Restart the secure server after generating the certificate with following the command:

/sbin/service httpd restart

25.9. Testing The Certificate

To test the test certificate installed by default, either a CA-signed certificate, or a self-signed certificate, point your Web browser to the following home page (replacing server.example.com with your domain name):

https://server.example.com

Note

Note the s after http. The https: prefix is used for secure HTTP transactions.

If you are using a CA-signed certificate from a well-known CA, your browser probably automatically accepts the certificate (without prompting you for input) and creates the secure connection. Your browser does not automatically recognize a test or a self-signed certificate, because the certificate is not signed by a CA. If you are not using a certificate from a CA, follow the instructions provided by your browser to accept the certificate.

25.10. Accessing The Server

To access your secure server, use a URL similar to the following:

https://server.example.com

Your non-secure server can be accessed using an URL similar to the following:

http://server.example.com

The standard port for secure Web communications is port 443. The standard port for non-secure Web communications is port 80. The secure server default configuration listens on both of the two standard ports. Therefore, do not need to specify the port number in a URL (the port number is assumed).

However, if you configure your server to listen on a non-standard port (for example, anything other than 80 or 443), you must specify the port number in every URL which is intended to connect to the server on the non-standard port.

For example, you may have configured your server so that you have a virtual host running non-secured on port 12331. Any URLs intended to connect to that virtual host must specify the port number in the URL. The following URL example attempts to connect to a non-secure server listening on port 12331:

Chapter 26. Authentication Configuration

When a user logs in to a Red Hat Enterprise Linux system, the username and password combination must be verified, or authenticated, as a valid and active user. Sometimes the information to verify the user is located on the local system, and other times the system defers the authentication to a user database on a remote system.

The Authentication Configuration Tool provides a graphical interface for configuring NIS, LDAP, and Hesiod to retrieve user information as well as for configuring LDAP, Kerberos, and SMB as authentication protocols.

Note

If you configured a medium or high security level during installation or with the Security Level Configuration Tool, network authentication methods, including NIS and LDAP, are not allowed through the firewall.

This chapter does not explain each of the different authentication types in detail. Instead, it explains how to use the Authentication Configuration Tool to configure them. For more information about the specific authentication types, refer to the Reference Guide.

To start the graphical version of the Authentication Configuration Tool from the desktop, select the Main Menu Button (on the Panel) => System Settings => Authentication or type the command system-config-authentication at a shell prompt (for example, in an XTerm or a GNOME terminal). To start the text-based version, type the command authconfig as root at a shell prompt.

Important

After exiting the authentication program, the changes made take effect immediately.

26.1. User Information

The User Information tab has several options. To enable an option, click the empty checkbox beside it. To disable an option, click the checkbox beside it to clear the checkbox. Click OK to exit the program and apply the changes.

Figure 26.1. User Information

The following list explains what each option configures:

Enable NIS Support — Select this option to configure the system as an NIS client which connects to an NIS server for user and password authentication. Click the Configure NIS button to specify the NIS domain and NIS server. If the NIS server is not specified, the daemon attempts to find it via broadcast.

The ypbind package must be installed for this option to work. If NIS support is enabled, the portmap and ypbind services are started and are also enabled to start at boot time.

Enable LDAP Support — Select this option to configure the system to retrieve user information via LDAP. Click the Configure LDAP button to specify the LDAP Search Base DN and LDAP Server. If Use TLS to encrypt connections is selected, Transport Layer Security is used to encrypt passwords sent to the LDAP server.

The openldap-clients package must be installed for this option to work.

For more information about LDAP, refer to the Reference Guide.

Enable Hesiod Support — Select this option to configure the system to retrieve information from a remote Hesiod database, including user information.

The hesiod package must be installed.

Winbind — Select this option to configure the system to connect to a Windows Active Directory or a Windows domain controller. User information can be accessed, as well as server authentication options can be configured.

Cache User Information — Select this option to enable the name service cache daemon (nscd) and configure it to start at boot time.

The nscd package must be installed for this option to work.

26.2. Authentication

The Authentication tab allows for the configuration of network authentication methods. To enable an option, click the empty checkbox beside it. To disable an option, click the checkbox beside it to clear the checkbox.

The openldap-clients package must be installed for this option to work. Refer to the Reference Guide for more information about LDAP.

Use Shadow Passwords — Select this option to store passwords in shadow password format in the /etc/shadow file instead of /etc/passwd. Shadow passwords are enabled by default during installation and are highly recommended to increase the security of the system.

The shadow-utils package must be installed for this option to work. For more information about shadow passwords, refer to the Users and Groups chapter in the Reference Guide.

Enable SMB Support — This option configures PAM to use an SMB server to authenticate users. Click the Configure SMB button to specify:

Workgroup — Specify the SMB workgroup to use.

Domain Controllers — Specify the SMB domain controllers to use.

Winbind — Select this option to configure the system to connect to a Windows Active Directory or a Windows domain controller. User information can be accessed, as well as server authentication options can be configured.

Use MD5 Passwords — Select this option to enable MD5 passwords, which allows passwords to be up to 256 characters instead of eight characters or less. It is selected by default during installation and is highly recommended for increased security.

26.3. Command Line Version

The Authentication Configuration Tool can also be run as a command line tool with no interface. The command line version can be used in a configuration script or a kickstart script. The authentication options are summarized in Table 26.1, “Command Line Options”.

Tip

These options can also be found in the authconfig man page or by typing authconfig --help at a shell prompt.

Table 26.1. Command Line Options

Option

Description

--enableshadow

Enable shadow passwords

--disableshadow

Disable shadow passwords

--enablemd5

Enable MD5 passwords

--disablemd5

Disable MD5 passwords

--enablenis

Enable NIS

--disablenis

Disable NIS

--nisdomain=<domain>

Specify NIS domain

--nisserver=<server>

Specify NIS server

--enableldap

Enable LDAP for user information

--disableldap

Disable LDAP for user information

--enableldaptls

Enable use of TLS with LDAP

--disableldaptls

Disable use of TLS with LDAP

--enableldapauth

Enable LDAP for authentication

--disableldapauth

Disable LDAP for authentication

--ldapserver=<server>

Specify LDAP server

--ldapbasedn=<dn>

Specify LDAP base DN

--enablekrb5

Enable Kerberos

--disablekrb5

Disable Kerberos

--krb5kdc=<kdc>

Specify Kerberos KDC

--krb5adminserver=<server>

Specify Kerberos administration server

--krb5realm=<realm>

Specify Kerberos realm

--enablekrb5kdcdns

Enable use of DNS to find Kerberos KDCs

--disablekrb5kdcdns

Disable use of DNS to find Kerberos KDCs

--enablekrb5realmdns

Enable use of DNS to find Kerberos realms

--disablekrb5realmdns

Disable use of DNS to find Kerberos realms

--enablesmbauth

Enable SMB

--disablesmbauth

Disable SMB

--smbworkgroup=<workgroup>

Specify SMB workgroup

--smbservers=<server>

Specify SMB servers

--enablewinbind

Enable winbind for user information by default

--disablewinbind

Disable winbind for user information by default

--enablewinbindauth

Enable winbindauth for authentication by default

--disablewinbindauth

Disable winbindauth for authentication by default

--smbsecurity=<user|server|domain|ads>

Security mode to use for Samba and winbind

--smbrealm=<STRING>

Default realm for Samba and winbind when security=ads

--smbidmapuid=<lowest-highest>

UID range winbind assigns to domain or ADS users

--smbidmapgid=<lowest-highest>

GID range winbind assigns to domain or ADS users

--winbindseparator=<\>

Character used to separate the domain and user part of winbind usernames if winbindusedefaultdomain is not enabled

--winbindtemplatehomedir=</home/%D/%U>

Directory that winbind users have as their home

--winbindtemplateprimarygroup=<nobody>

Group that winbind users have as their primary group

--winbindtemplateshell=</bin/false>

Shell that winbind users have as their default login shell

--enablewinbindusedefaultdomain

Configures winbind to assume that users with no domain in their usernames are domain users

--disablewinbindusedefaultdomain

Configures winbind to assume that users with no domain in their usernames are not domain users

--winbindjoin=<Administrator>

Joins the winbind domain or ADS realm now as this administrator

--enablewins

Enable WINS for hostname resolution

--disablewins

Disable WINS for hostname resolution

--enablehesiod

Enable Hesiod

--disablehesiod

Disable Hesiod

--hesiodlhs=<lhs>

Specify Hesiod LHS

--hesiodrhs=<rhs>

Specify Hesiod RHS

--enablecache

Enable nscd

--disablecache

Disable nscd

--nostart

Do not start or stop the portmap, ypbind, or nscd services even if they are configured

--kickstart

Do not display the user interface

--probe

Probe and display network defaults

Part V. System Configuration

Part of a system administrator's job is configuring the system for various tasks, types of users, and hardware configurations. This section explains how to configure a Red Hat Enterprise Linux system.

When normal (non-root) users log into a computer locally, they are given two types of special permissions:

They can run certain programs that they would not otherwise be able to run

They can access certain files (normally special device files used to access diskettes, CD-ROMs, and so on) that they would not otherwise be able to access

Since there are multiple consoles on a single computer and multiple users can be logged into the computer locally at the same time, one of the users has to essentially win the race to access the files. The first user to log in at the console owns those files. Once the first user logs out, the next user who logs in owns the files.

In contrast, every user who logs in at the console is allowed to run programs that accomplish tasks normally restricted to the root user. If X is running, these actions can be included as menu items in a graphical user interface. As shipped, the console-accessible programs include halt, poweroff, and reboot.

27.1. Disabling Shutdown Via Ctrl+Alt+Del

By default, /etc/inittab specifies that your system is set to shutdown and reboot in response to a Ctrl+Alt+Del key combination used at the console. To completely disable this ability, comment out the following line in /etc/inittab by putting a hash mark (#) in front of it:

ca::ctrlaltdel:/sbin/shutdown -t3 -r now

Alternatively, you may want to allow certain non-root users the right to shutdown or reboot the system from the console using Ctrl+Alt+Del. You can restrict this privilege to certain users, by taking the following steps:

Add the -a option to the /etc/inittab line shown above, so that it reads:

ca::ctrlaltdel:/sbin/shutdown -a -t3 -r now

The -a flag tells shutdown to look for the /etc/shutdown.allow file.

Create a file named shutdown.allow in /etc. The shutdown.allow file should list the usernames of any users who are allowed to shutdown the system using Ctrl+Alt+Del. The format of the shutdown.allow file is a list of usernames, one per line, like the following:

stephen
jack
sophie

According to this example shutdown.allow file, the users stephen, jack, and sophie are allowed to shutdown the system from the console using Ctrl+Alt+Del. When that key combination is used, the shutdown -a command in /etc/inittab checks to see if any of the users in /etc/shutdown.allow (or root) are logged in on a virtual console. If one of them is, the shutdown of the system continues; if not, an error message is written to the system console instead.

For more information on shutdown.allow, refer to the shutdown man page.

27.2. Disabling Console Program Access

To disable access by users to console programs, run the following command as root:

rm -f /etc/security/console.apps/*

In environments where the console is otherwise secured (BIOS and boot loader passwords are set, Ctrl+Alt+Delete is disabled, the power and reset switches are disabled, and so forth), you may not want to allow any user at the console to run poweroff, halt, and reboot, which are accessible from the console by default.

27.3. Defining the Console

The pam_console.so module uses the /etc/security/console.perms file to determine the permissions for users at the system console. The syntax of the file is very flexible; you can edit the file so that these instructions no longer apply. However, the default file has a line that looks like this:

<console>=tty[0-9][0-9]* vc/[0-9][0-9]* :[0-9]\.[0-9] :[0-9]

When users log in, they are attached to some sort of named terminal, either an X server with a name like :0 or mymachine.example.com:1.0, or a device like /dev/ttyS0 or /dev/pts/2. The default is to define that local virtual consoles and local X servers are considered local, but if you want to consider the serial terminal next to you on port /dev/ttyS1 to also be local, you can change that line to read:

Then, when you log in at the console, you are given ownership of the /dev/scanner device with the permissions of 0600 (readable and writable by you only). When you log out, the device is owned by root and still has the permissions 0600 (now readable and writable by root only).

27.5. Enabling Console Access for Other Applications

To make other applications accessible to console users, a bit more work is required.

First of all, console access only works for applications which reside in /sbin/ or /usr/sbin/, so the application that you wish to run must be there. After verifying that, do the following steps:

Create a link from the name of your application, such as our sample foo program, to the /usr/bin/consolehelper application:

cd /usr/binln -s consolehelper foo

Create the file /etc/security/console.apps/foo:

touch /etc/security/console.apps/foo

Create a PAM configuration file for the foo service in /etc/pam.d/. An easy way to do this is to start with a copy of the halt service's PAM configuration file, and then modify the file if you want to change the behavior:

cp /etc/pam.d/halt /etc/pam.d/foo

Now, when /usr/bin/foo is executed, consolehelper is called, which authenticates the user with the help of /usr/sbin/userhelper. To authenticate the user, consolehelper asks for the user's password if /etc/pam.d/foo is a copy of /etc/pam.d/halt (otherwise, it does precisely what is specified in /etc/pam.d/foo) and then runs /usr/sbin/foo with root permissions.

In the PAM configuration file, an application can be configured to use the pam_timestamp module to remember (or cache) a successful authentication attempt. When an application is started and proper authentication is provided (the root password), a timestamp file is created. By default, a successful authentication is cached for five minutes. During this time, any other application that is configured to use pam_timestamp and run from the same session is automatically authenticated for the user — the user does not have to enter the root password again.

This module is included in the pam package. To enable this feature, the PAM configuration file in etc/pam.d/ must include the following lines:

The first line that begins with auth should be after any other auth sufficient lines, and the line that begins with session should be after any other session optional lines.

If an application configured to use pam_timestamp is successfully authenticated from the Main Menu Button (on the Panel), the
icon is displayed in the notification area of the panel if you are running the GNOME or KDE desktop environment. After the authentication expires (the default is five minutes), the icon disappears.

The user can select to forget the cached authentication by clicking on the icon and selecting the option to forget authentication.

27.6. The floppy Group

If, for whatever reason, console access is not appropriate for you and your non-root users are required access to your system's diskette drive, this can be done using the floppy group. Add the user(s) to the floppy group using the tool of your choice. For example, the gpasswd command can be used to add user fred to the floppy group:

gpasswd -a fred floppy

Now, user fred is able to access the system's diskette drive from the console.

Chapter 28. Date and Time Configuration

The Time and Date Properties Tool allows the user to change the system date and time, to configure the time zone used by the system, and to setup the Network Time Protocol (NTP) daemon to synchronize the system clock with a time server.

You must be running the X Window System and have root privileges to use the tool. There are three ways to start the application:

From the desktop, go to Applications (the main menu on the
panel) => System Settings => Date & Time

From the desktop, right-click on the time in the toolbar and select Adjust Date and Time.

Type the command system-config-date, system-config-time, or dateconfig at a shell prompt (for example, in an XTerm or a GNOME terminal).

28.1. Time and Date Properties

To change the date, use the arrows to the left and right of the month to change the month, use the arrows to the left and right of the year to change the year, and click on the day of the week to change the day of the week.

To change the time, use the up and down arrow buttons beside the Hour, Minute, and Second in the Time section.

Clicking the OK button applies any changes made to the date and time, the NTP daemon settings, and the time zone settings. It also exits the program.

28.2. Network Time Protocol (NTP) Properties

The Network Time Protocol (NTP) daemon synchronizes the system clock with a remote time server or time source. The application allows you to configure an NTP daemon to synchronize your system clock with a remote server. To enable this feature, select Enable Network Time Protocol. This enables the NTP Servers list and other options. You can choose one of the predefined servers, edit a predefined server by clicking the Edit or add a new server name by clicking Add. Your system does not start synchronizing with the NTP server until you click OK. After clicking OK, the configuration is saved and the NTP daemon is started (or restarted if it is already running).

Clicking the OK button applies any changes made to the date and time, the NTP daemon settings, and the time zone settings. It also exits the program.

28.3. Time Zone Configuration

To configure the system time zone, click the Time Zone tab. The time zone can be changed by either using the interactive map or by choosing the desired time zone from the list below the map. To use the map, click on the desired region. The map zooms into the region selected, after which you may choose the city specific to your time zone. A red X appears and the time zone selection changes in the list below the map.

Alternatively, you can also use the list below the map. In the same way that the map lets you choose a region before choosing a city, the list of time zones is now a treelist, with cities and countries grouped within their specific continents. Non-geographic time zones have also been added to address needs in the scientific community.

Click OK to apply the changes and exit the program.

Figure 28.3. Timezone Properties

If your system clock is set to use UTC, select the System clock uses UTC option. UTC stands for the Universal Time, Coordinated, also known as Greenwich Mean Time (GMT). Other time zones are determined by adding or subtracting from the UTC time.

Chapter 29. Keyboard Configuration

The installation program allows users to configure a keyboard layout for their systems. To configure a different keyboard layout after installation, use the Keyboard Configuration Tool.

To start the Keyboard Configuration Tool, select Applications (the main menu on the
panel) => System Settings => Keyboard, or type the command system-config-keyboard at a shell prompt.

Figure 29.1. Keyboard Configuration

Select a keyboard layout from the list (for example, U.S. English) and click OK. For changes to take effect, you should log out of your graphical desktop session and log back in.

Chapter 30. Mouse Configuration

The installation program allows users to select the type of mouse connected to the system. To configure a different mouse type for the system, use the Mouse Configuration Tool.

To start the Mouse Configuration Tool, type the command system-config-mouse at a shell prompt (for example, in an XTerm or GNOME terminal). If the X Window System is not running, the text-based version of the tool is started.

Figure 30.1. Mouse Configuration

Select the new mouse type for the system. If the specific mouse model is not listed, select one of the Generic entries, based on the mouse's number of buttons and its interface. If there is not an exact match, select the generic match that is most compatible with the system and the mouse.

Tip

Select the Generic - Wheel Mouse entry, with the proper mouse port, to enable the scroll button on the mouse.

The scroll button on a wheel mouse can be used as the middle mouse button for cutting text, pasting text, and other middle mouse button functions. If the mouse only has two buttons, select Emulate 3 buttons to use a two-button mouse as a three-button mouse. When this option enabled, clicking the two mouse buttons simultaneously emulates a middle mouse button click.

If a serial port mouse is selected, click the Serial devices button to configure the correct serial device number, such as /dev/ttyS0 for the mouse.

Click OK to save the new mouse type. The selection is written to the file /etc/sysconfig/mouse, and the console mouse service, gpm is restarted. The changes are also written to the X Window System configuration file /etc/X11/xorg.conf; however, the mouse type change is not automatically applied to the current X session. To enable the new mouse type, log out of the graphical desktop and log back in.

Tip

To reset the order of the mouse buttons for a left-handed user, go to Applications (the main menu on the
panel) => Preferences => Mouse, and select Left-handed mouse for the mouse orientation.

Chapter 31. X Window System Configuration

During installation, the system's monitor, video card, and display settings are configured. To change any of these settings after installation, use the X Configuration Tool.

To start the X Configuration Tool, go to Applications (the main menu on the
panel) => Administration => Display, or type the command system-config-display at a shell prompt (for example, in an XTerm or GNOME terminal). If the X Window System is not running, a small version of X is started to run the program.

After changing any of the settings, log out of the graphical desktop and log back in to enable the changes.

31.1. Display Settings

The Settings tab allows users to change the resolution and color depth. The display of a monitor consists of tiny dots called pixels. The number of pixels displayed at one time is called the resolution. For example, the resolution 1024x768 means that 1024 horizontal pixels and 768 vertical pixels are used. The higher the resolution values, the more images the monitor can display at one time.

The color depth of the display determines how many possible colors are displayed. A higher color depth means more contrast between colors.

Figure 31.1. Display Settings

31.2. Display Hardware Settings

When the X Configuration Tool is started, it probes the monitor and video card. If the hardware is probed properly, the information for it is shown on the Hardware tab as shown in Figure 31.2, “Display Hardware Settings”.

Figure 31.2. Display Hardware Settings

To change the monitor type or any of its settings, click the corresponding Configure button. To change the video card type or any of its settings, click the Configure button beside its settings.

To configure the second monitor type, click the corresponding Configure button. You can also configure the other Dual head settings by using the corresponding drop-down list.

For the Desktop layout option, selecting Spanning Desktops allows both monitors to use an enlarged usable workspace. Selecting Individual Desktops shares the mouse and keyboard among the displays, but restricts windows to a single display.

The control of users and groups is a core element of Red Hat Enterprise Linux system administration.

Users can be either people (meaning accounts tied to physical users) or accounts which exist for specific applications to use.

Groups are logical expressions of organization, tying users together for a common purpose. Users within a group can read, write, or execute files owned by that group.

Each user and group has a unique numerical identification number called a userid (UID) and a groupid (GID), respectively.

A user who creates a file is also the owner and group owner of that file. The file is assigned separate read, write, and execute permissions for the owner, the group, and everyone else. The file owner can be changed only by the root user, and access permissions can be changed by both the root user and file owner.

32.1. User and Group Configuration

The User Manager allows you to view, modify, add, and delete local users and groups.

To use the User Manager, you must be running the X Window System, have root privileges, and have the system-config-users RPM package installed. To start the User Manager from the desktop, go to Applications (the main menu on the
panel) => Administration => Users & Groups. You can also type the command system-config-users at a shell prompt (for example, in an XTerm or a GNOME terminal).

Figure 32.1. User Manager

To view a list of local users on the system, click the Users tab. To view a list of local groups on the system, click the Groups tab.

To find a specific user or group, type the first few letters of the name in the Search filter field. Press Enter or click the Apply filter button. The filtered list is displayed.

To sort the users or groups, click on the column name. The users or groups are sorted according to the value of that column.

Red Hat Enterprise Linux reserves user IDs below 500 for system users. By default, User Manager does not display system users. To view all users, including the system users, go to Edit => Preferences and uncheck Hide system users and groups from the dialog box.

32.1.1. Adding a New User

To add a new user, click the Add User button. A window as shown in Figure 32.2, “New User” appears. Type the username and full name for the new user in the appropriate fields. Type the user's password in the Password and Confirm Password fields. The password must be at least six characters.

Tip

It is advisable to use a much longer password, as this makes it more difficult for an intruder to guess it and access the account without permission. It is also recommended that the password not be based on a dictionary term; use a combination of letters, numbers and special characters.

Select a login shell. If you are not sure which shell to select, accept the default value of /bin/bash. The default home directory is /home/<username>/. You can change the home directory that is created for the user, or you can choose not to create the home directory by unselecting Create home directory.

If you select to create the home directory, default configuration files are copied from the /etc/skel/ directory into the new home directory.

Red Hat Enterprise Linux uses a user private group (UPG) scheme. The UPG scheme does not add or change anything in the standard UNIX way of handling groups; it offers a new convention. Whenever you create a new user, by default, a unique group with the same name as the user is created. If you do not want to create this group, unselect Create a private group for the user.

To specify a user ID for the user, select Specify user ID manually. If the option is not selected, the next available user ID above 500 is assigned to the new user. Because Red Hat Enterprise Linux reserves user IDs below 500 for system users, it is not advisable to manually assign user IDs 1-499.

32.1.2. Modifying User Properties

To view the properties of an existing user, click on the Users tab, select the user from the user list, and click Properties from the menu (or choose File => Properties from the pulldown menu). A window similar to Figure 32.3, “User Properties” appears.

Figure 32.3. User Properties

The User Properties window is divided into multiple tabbed pages:

User Data — Shows the basic user information configured when you added the user. Use this tab to change the user's full name, password, home directory, or login shell.

Account Info — Select Enable account expiration if you want the account to expire on a certain date. Enter the date in the provided fields. Select Local password is locked to lock the user account and prevent the user from logging into the system.

Password Info — Displays the date that the user's password last changed. To force the user to change passwords after a certain number of days, select Enable password expiration and enter a desired value in the Days before change required: field. The number of days before the user's password expires, the number of days before the user is warned to change passwords, and days before the account becomes inactive can also be changed.

Groups — Allows you to view and configure the Primary Group of the user, as well as other groups that you want the user to be a member of.

32.1.3. Adding a New Group

To add a new user group, click the Add Group button. A window similar to Figure 32.4, “New Group” appears. Type the name of the new group to create. To specify a group ID for the new group, select Specify group ID manually and select the GID. Note that Red Hat Enterprise Linux also reserves group IDs lower than 500 for system groups.

Figure 32.4. New Group

Click OK to create the group. The new group appears in the group list.

32.1.4. Modifying Group Properties

To view the properties of an existing group, select the group from the group list and click Properties from the menu (or choose File => Properties from the pulldown menu). A window similar to Figure 32.5, “Group Properties” appears.

Figure 32.5. Group Properties

The Group Users tab displays which users are members of the group. Use this tab to add or remove users from the group. Click OK to save your changes.

32.2. User and Group Management Tools

Managing users and groups can be a tedious task; this is why Red Hat Enterprise Linux provides tools and conventions to make them easier to manage.

<comment> can be replaced with any string. This option is generally used to specify the full name of a user.

-d<home-dir>

Home directory to be used instead of default /home/<username>/

-e<date>

Date for the account to be disabled in the format YYYY-MM-DD

-f<days>

Number of days after the password expires until the account is disabled. If 0 is specified, the account is disabled immediately after the password expires. If -1 is specified, the account is not be disabled after the password expires.

-g<group-name>

Group name or group number for the user's default group. The group must exist prior to being specified here.

-G<group-list>

List of additional (other than default) group names or group numbers, separated by commas, of which the user is a member. The groups must exist prior to being specified here.

-m

Create the home directory if it does not exist.

-M

Do not create the home directory.

-n

Do not create a user private group for the user.

-r

Create a system account with a UID less than 500 and without a home directory

Specifies the minimum number of days between which the user must change passwords. If the value is 0, the password does not expire.

-M<days>

Specifies the maximum number of days for which the password is valid. When the number of days specified by this option plus the number of days specified with the -d option is less than the current day, the user must change passwords before using the account.

-d<days>

Specifies the number of days since January 1, 1970 the password was changed

-I<days>

Specifies the number of inactive days after the password expiration before locking the account. If the value is 0, the account is not locked after the password expires.

-E<date>

Specifies the date on which the account is locked, in the format YYYY-MM-DD. Instead of the date, the number of days since January 1, 1970 can also be used.

-W<days>

Specifies the number of days before the password expiration date to warn the user.

Tip

If the chage command is followed directly by a username (with no options), it displays the current password aging values and allows them to be changed.

You can configure a password to expire the first time a user logs in. This forces users to change passwords the first time they log in.

Note

This process will not work if the user logs in using the SSH protocol.

Lock the user password — If the user does not exist, use the useradd command to create the user account, but do not give it a password so that it remains locked.

If the password is already enabled, lock it with the command:

usermod -L username

Force immediate password expiration — Type the following command:

chage -d 0 username

This command sets the value for the date the password was last changed to the epoch (January 1, 1970). This value forces immediate password expiration no matter what password aging policy, if any, is in place.

Unlock the account — There are two common approaches to this step. The administrator can assign an initial password or assign a null password.

Warning

Do not use the passwd command to set the password as it disables the immediate password expiration just configured.

To assign an initial password, use the following steps:

Start the command line Python interpreter with the python command. It displays the following:

At the prompt, type the following commands. Replace <password> with the password to encrypt and <salt> with a random combination of at least 2 of the following: any alphanumeric character, the slash (/) character or a dot (.):

import crypt; print crypt.crypt("<password>","<salt>")

The output is the encrypted password, similar to '12CsGd8FRcMSM'.

Press Ctrl-D to exit the Python interpreter.

At the shell, enter the following command (replacing <encrypted-password> with the encrypted output of the Python interpreter):

usermod -p "<encrypted-password>" <username>

Alternatively, you can assign a null password instead of an initial password. To do this, use the following command:

usermod -p "" username

Warning

Using a null password, while convenient, is a highly unsecure practice, as any third party can log in first an access the system using the unsecure username. Always make sure that the user is ready to log in before unlocking an account with a null password.

In either case, upon initial log in, the user is prompted for a new password.

32.2.5. Explaining the Process

The following steps illustrate what happens if the command useradd juan is issued on a system that has shadow passwords enabled:

A new line for juan is created in /etc/passwd. The line has the following characteristics:

It begins with the username juan.

There is an x for the password field indicating that the system is using shadow passwords.

A UID greater than 499 is created. (Under Red Hat Enterprise Linux, UIDs and GIDs below 500 are reserved for system use.)

A GID greater than 499 is created.

The optional GECOS information is left blank.

The home directory for juan is set to /home/juan/.

The default shell is set to /bin/bash.

A new line for juan is created in /etc/shadow. The line has the following characteristics:

It begins with the username juan.

Two exclamation points (!!) appear in the password field of the /etc/shadow file, which locks the account.

Note

If an encrypted password is passed using the -p flag, it is placed in the /etc/shadow file on the new line for the user.

The password is set to never expire.

A new line for a group named juan is created in /etc/group. A group with the same name as a user is called a user private group. For more information on user private groups, refer to Section 32.1.1, “Adding a New User”.

The line created in /etc/group has the following characteristics:

It begins with the group name juan.

An x appears in the password field indicating that the system is using shadow group passwords.

The GID matches the one listed for user juan in /etc/passwd.

A new line for a group named juan is created in /etc/gshadow. The line has the following characteristics:

It begins with the group name juan.

An exclamation point (!) appears in the password field of the /etc/gshadow file, which locks the group.

All other fields are blank.

A directory for user juan is created in the /home/ directory. This directory is owned by user juan and group juan. However, it has read, write, and execute privileges only for the user juan. All other permissions are denied.

The files within the /etc/skel/ directory (which contain default user settings) are copied into the new /home/juan/ directory.

At this point, a locked account called juan exists on the system. To activate it, the administrator must next assign a password to the account using the passwd command and, optionally, set password aging guidelines.

32.5. User Private Groups

A UPG is created whenever a new user is added to the system. A UPG has the same name as the user for which it was created and that user is the only member of the UPG.

UPGs make it safe to set default permissions for a newly created file or directory, allowing both the user and the group of that user to make modifications to the file or directory.

The setting which determines what permissions are applied to a newly created file or directory is called a umask and is configured in the /etc/bashrc file. Traditionally on UNIX systems, the umask is set to 022, which allows only the user who created the file or directory to make modifications. Under this scheme, all other users, including members of the creator's group, are not allowed to make any modifications. However, under the UPG scheme, this "group protection" is not necessary since every user has their own private group.

32.5.1. Group Directories

Many IT organizations like to create a group for each major project and then assign people to the group if they need to access that project's files. Using this traditional scheme, managing files has been difficult; when someone creates a file, it is associated with the primary group to which they belong. When a single person works on multiple projects, it is difficult to associate the right files with the right group. Using the UPG scheme, however, groups are automatically assigned to files created within a directory with the setgid bit set. The setgid bit makes managing group projects that share a common directory very simple because any files a user creates within the directory are owned by the group which owns the directory.

Let us say, for example, that a group of people need to work on files in the /usr/share/emacs/site-lisp/ directory. Some people are trusted to modify the directory, but certainly not everyone is trusted. First create an emacs group, as in the following command:

/usr/sbin/groupadd emacs

To associate the contents of the directory with the emacs group, type:

chown -R root.emacs /usr/share/emacs/site-lisp

Now, it is possible to add the proper users to the group with the gpasswd command:

/usr/bin/gpasswd -a <username> emacs

To allow users to create files within the directory, use the following command:

chmod 775 /usr/share/emacs/site-lisp

When a user creates a new file, it is assigned the group of the user's default private group. Next, set the setgid bit, which assigns everything created in the directory the same group permission as the directory itself (emacs). Use the following command:

chmod 2775 /usr/share/emacs/site-lisp

At this point, because the default umask of each user is 002, all members of the emacs group can create and edit files in the /usr/share/emacs/site-lisp/ directory without the administrator having to change file permissions every time users write new files.

32.6. Shadow Passwords

In multiuser environments it is very important to use shadow passwords (provided by the shadow-utils package). Doing so enhances the security of system authentication files. For this reason, the installation program enables shadow passwords by default.

The following lists the advantages pf shadow passwords have over the traditional way of storing passwords on UNIX-based systems:

Improves system security by moving encrypted password hashes from the world-readable /etc/passwd file to /etc/shadow, which is readable only by the root user.

Stores information about password aging.

Allows the use the /etc/login.defs file to enforce security policies.

Most utilities provided by the shadow-utils package work properly whether or not shadow passwords are enabled. However, since password aging information is stored exclusively in the /etc/shadow file, any commands which create or modify password aging information do not work.

The following is a list of commands which do not work without first enabling shadow passwords:

chage

gpasswd

/usr/sbin/usermod-e or -f options

/usr/sbin/useradd-e or -f options

32.7. Additional Resources

For more information about users and groups, and tools to manage them, refer to the following resources.

32.7.1. Installed Documentation

Related man pages — There are a number of man pages for the various applications and configuration files involved with managing users and groups. Some of the more important man pages have been listed here:

Red Hat Enterprise Linux 4 uses the Common Unix Printing System (CUPS). If a system was upgraded from a previous Red Hat Enterprise Linux version that used CUPS, the upgrade process preserves the configured queues.

Using Printer Configuration Tool requires root privileges. To start the application, select Applications (the main menu on the
panel) => Administration => Printing, or type the command system-config-printer at a shell prompt.

Figure 33.1. Printer Configuration Tool

The following types of print queues can be configured:

AppSocket/HP JetDirect — a printer connected directly to the network through HP JetDirect or Appsocket interface instead of a computer.

Internet Printing Protocol (IPP) — a printer that can be accessed over a TCP/IP network via the Internet Printing Protocol (for example, a printer attached to another Red Hat Enterprise Linux system running CUPS on the network).

LPD/LPR Host or Printer — a printer attached to a different UNIX system that can be accessed over a TCP/IP network (for example, a printer attached to another Red Hat Enterprise Linux system running LPD on the network).

Networked Windows (SMB) — a printer attached to a different system which is sharing a printer over an SMB network (for example, a printer attached to a Microsoft Windows™ machine).

Networked JetDirect — a printer connected directly to the network through HP JetDirect instead of a computer.

Important

If you add a new print queue or modify an existing one, you must apply the changes for them to take effect.

Clicking the Apply button prompts the printer daemon to restart with the changes you have configured.

Clicking the Revert button discards unapplied changes.

33.1. Adding a Local Printer

To add a local printer, such as one attached through a parallel port or USB port on your computer, click the New Printer button in the main Printer Configuration Tool window to display the window in Figure 33.2, “Adding a Printer”.

Figure 33.2. Adding a Printer

Click Forward to proceed.

Enter a unique name for the printer in the Printer Name field. The printer name can contain letters, numbers, dashes (-), and underscores (_); it must not contain any spaces.

You can also use the Description and Location fields to further distinguish this printer from others that may be configured on your system. Both of these fields are optional, and may contain spaces.

Click Forward to open the New Printer dialogue (refer to Figure 33.3, “Adding a Local Printer”). If the printer has been automatically detected, the printer model appears in Select Connection. Select the printer model and click Forward to continue.

If the device does not automatically appear, select the device to which the printer is connected (such as LPT #1 or Serial Port #1) in Select Connection.

33.2. Adding an IPP Printer

An IPP printer is a printer attached to a different system on the same TCP/IP network. The system this printer is attached to may either be running CUPS or simply configured to use IPP.

If a firewall is enabled on the printer server, then the firewall should be configured to allow send / receive connections on the incoming UDP port 631. If a firewall is enabled on on the client (the system sending the print request) then the firewall must be allowed to accept and create connections through port 631.

You can add a networked IPP printer by clicking the New Printer button in the main Printer Configuration Tool window to display the window in Figure 33.2, “Adding a Printer”. Enter the Printer Name (printer names cannot contain spaces and may contain letters, numbers, dashes (-), and underscores (_)), Description, and Location to distinguish this printer from others that you may configure on your system. Click Forward to proceed.

In the window shown in Figure 33.4, “Adding an IPP Printer”, enter the hostname of the IPP printer in the Hostname field as well as a unique name for the printer in the Printername field.

33.3. Adding a Samba (SMB) Printer

You can add a Samba (SMB) based printer share by clicking the New Printer button in the main Printer Configuration Tool window to display the window in Figure 33.2, “Adding a Printer”. Enter a unique n